Russia's invasion of Ukraine has entered its 13th day, with Moscow troops ramping up attacks on several major cities, including Kyiv. 

Russian forces have reportedly launched hundreds of missiles and artillery attacks on residential areas of Chernihiv and Mykolaiv, with Ukrainian forces also defending the port city of Odesa from invading ships. 

The Ukrainian government has accused Russia of breaking a ceasefire agreement, by shelling a route intended to allow civilians to escape the besieged city of Mariupol. 

Residents of the port city are under intense bombardment by Russian troops, and also living without heat, water, sanitary systems or phones. 

Around two million people have fled Ukraine since the war began less than two weeks ago, the UN refugee agency has reported. 

Meanwhile, military experts said Russia is overcoming its logistics problems and could mount an assault on Kyiv within a matter of days. 

Follow our live updates below: 

Russian debt default 'imminent' 

A Russian default is "imminent", American credit rating agency Fitch has warned. 

The agency today downgraded Russia's sovereign rating by six points from "B" to "C", moving it into junk territory, meaning there's a bigger chance the government won't be able to pay back its debts. 

Fitch cited the decision by Russian President Vladimir Putin to allow certain foreign debts to be paid off in the plummeting rouble as a red flag. The decree allows entities in Russia to pay back debt in roubles if it is owed to a creditor from "countries that engage in hostile activities". 

That's raised the spectre of Russia's first default since 1998. 

"More generally, the further ratcheting up of sanctions, and proposals that could limit trade in energy, increase the probability of a policy response by Russia that includes at least selective non-payment of its sovereign debt obligations," ratings agency Fitch said. 

Foreigners hold about $29 billion in Russian bonds. Russia is due to pay $107 million in coupons across two bonds on March 16. 

Credit agency Moody's has also slashed Russia's sovereign rating to junk. 

The alert was issued as the rouble sinks against the US dollar. 

One dollar now buys 130 roubles, with the currency sinking by about 50 per cent since the invasion of Ukraine began on February 24. 

And it could sink further. 

"The combination of Western sanctions, the rising risk of default and the incentive to divest from rouble-denominated assets will likely further weigh on the currency," Ipek Ozkardeskaya, senior analyst at Swissquote Bank, told Reuters. 

Russia's economy has been shattered by harsh economic sanctions imposed by the West in the wake of the Putin-led invasion of Ukraine. 

Russian banks have been blocked from SWIFT, the global banking messaging system that enables transactions everywhere. Being kicked out means banks are unable to process payments with each other or overseas in any useful time frame. 

Putin's 'extremely unusual' move terrifying the world 

Putin is using nuclear "blackmail" to keep the international community from interfering in his Ukraine invasion, the head of the Nobel prize-winning group ICAN said. 

"This is one of the scariest moments really when it comes to nuclear weapons," Beatrice Fihn, who leads the International Campaign to Abolish Nuclear Weapons, told AFP in an interview Tuesday. 

The 40-year-old Swede, who has spearheaded the group's global efforts to ban the weapons of mass destruction since 2013, said she had never in her lifetime seen the nuclear threat level so high. 

"It is incredibly worrying and overwhelming." 

Just days after Russia launched its full-scale invasion of its pro-Western neighbour on February 24, Putin ordered his country's nuclear forces to be put on high alert, sparking global alarm. 

Addressing the US Congress on Tuesday, Avril Haines, US Director of National Intelligence, described Putin's move as "extremely unusual". 

"We have not seen a public announcement from the Russians regarding a heightened nuclear alert status since the 1960s," she pointed out. 

Fihn described the move as "extremely dangerous". 

"Not only is this meant to instil fear in the whole world; it's also meant to scare anyone from helping in Ukraine," he said. 

Pentagon says Poland's jet offer for Ukraine 'not tenable' 

The Pentagon has rejected Poland's surprise announcement that it would give the United States its MiG-29 fighter jets for use by Ukraine, a rare display of disharmony by NATO allies seeking to boost Ukrainian fighters, while avoiding getting caught up in a wider war with Russia. 

Pentagon spokesman John Kirby said Poland's declaration it intended to deliver the 28 jets to the US Ramstein Air Base in Germany raised the concerning prospect of warplanes departing from a US and NATO base to fly into airspace contested with Russia in the Ukraine conflict. 

"We will continue to consult with Poland and our other NATO allies about this issue and the difficult logistical challenges it presents, but we do not believe Poland's proposal is a tenable one," Kirby said in a statement. 

The proposed gift of more warplanes would be a morale booster for Ukrainians under pounding Russian assault for nearly two weeks. But it also raises the risk of the war expanding beyond Ukraine. 

Russia has declared that supporting Ukraine's air force would be tantamount to joining the war, and could spur retaliation. 

'Please help our nation': Former Ukrainian MP Hopko Hanna's heartbreaking interview 

Former Ukrainian MP Hopko Hanna broke down in tears during a heartbreaking interview with MSNBC. 

"This is about humanity," she said through tears, pleading once again with Biden and Congress to impose a no-fly zone over Ukraine. 

Staff at nuclear power plant 'tortured' by Russian troops 

Ukraine's energy minister Herman Halushchenko says Russian military units are "torturing" staff at the Zaporizhzhia Nuclear Power Plant in order to force them into making a public statement. 

He claims staff have been "held hostage for four days". 

"There are about 500 Russian soldiers and 50 units of heavy equipment inside the station. The employees of the station are physically and psychologically exhausted," Halushchenko said. 

More worrying developments from Chernobyl 

Ukrainian First Lady posts heartbreaking open letter 

In an open letter to the world media, First Lady of Ukraine Olena Zelenska has detailed some of the atrocities committed by Russian troops against civilians, particularly children, in Ukraine. 

"On February 24th, we all woke up to the announcement of a Russian invasion. Tanks crossed the Ukrainian border, planes entered our airspace, missile launchers surrounded our cities," she wrote. 

"Despite assurances from Kremlin-backed propaganda outlets, who call this a 'special operation' – it is, in fact, the mass murder of Ukrainian civilians. 

"Perhaps the most terrifying and devastating of this invasion are the child casualties. Eight-year-old Alice who died on the streets of Okhtyrka while her grandfather tried to protect her. Or Polina from Kyiv, who died in the shelling with her parents. 14-year-old Arseniy was hit in the head by wreckage, and could not be saved because an ambulance could not get to him on time because of intense fires. 

"When Russia says that it is 'not waging war against civilians,' I call out the names of these murdered children first," the First Lady added. 

"Our women and children now live in bomb shelters and basements. You have most likely all seen these images from Kyiv and Kharkiv metro stations, where people lie on the floors with their children and pets – trapped beneath. These are just consequences of war for some, for Ukrainians it now a horrific reality. In some cities families cannot get out of the bomb shelters for several days in a row because of the indiscriminate and deliberate bombing and shelling of civilian infrastructure. 

"The first newborn of the war, saw the concrete ceiling of the basement, their first breath was the acrid air of the underground, and they were greeted by a community trapped and terrorized. At this point, there are several dozen children who have never known peace in their lives. 

"This war is being waged against the civilian population, and not just through shelling." 

She continues her open letter in her Instagram images, calling on world media to keep detailing and showing images of what is happening in Ukraine. 

Zelenska also repeated the Ukrainian government's multiple appeals for the sky above the country to be closed. 

"Close the sky and we will manage the war on the ground ourselves," she wrote. 

"This is a war in Europe, close to the EU borders. Ukraine is stopping the force that may aggressively enter your cities tomorrow under the pretext of saving civilians," Zelenska added. 

"If we don't stop Putin, who threatens to start a nuclear war, there will be no safe place in the world for any of us." 

Putin likely to 'escalate' situation 

Despite Russia facing continued setbacks in its invasion of the Ukraine, officials have warned Vladimir Putin is unlikely to back down. 

Speaking to the House Intelligence Committee, US Director of National Intelligence Avril Haines said the world should expect the Russian leader to "escalate" the conflict. 

"Our analysts assess that Putin is unlikely to be deterred by such setbacks and instead may escalate, essentially doubling down to achieve Ukrainian disarmament, neutrality [and] to prevent it from further integrating with the US and NATO if it doesn't reach some diplomatic negotiation," she said. 

Russian forces have been met with fierce resistance from Ukraine and the country has been hit hard by repeated sanctions from the west. 

"We assess Putin feels aggrieved the West does not give him proper deference and perceives this as a war he cannot afford to lose," Ms Haines said. 

"But what he might be willing to accept as a victory may change over time given the significant costs he is incurring." 

She added Putin "probably" still has confidence that his forces can defeat Ukraine, but is using the threat of nuclear weapons in order to "prevent Western support from tipping the balance and forcing a conflict with Nato." 

"Russia's failure to rapidly seize Kyiv and overwhelm Ukrainian forces has deprived Moscow of the quick military victory that it probably had originally expected would prevent the United States and Nato from being able to provide meaningful military aid to Ukraine," Ms Haines said. 

Bioweapon rumour hints at Putin's next move 

The United States said Tuesday it was working with Ukraine to prevent invading Russian forces from seizing biological research material amid concern governments or unscrupulous actors might try to use such items to create bioweapons. 

"Ukraine has biological research facilities, which in fact we are now quite concerned Russian troops, Russian forces, may be seeking to gain control of," senior State Department official Victoria Nuland told US lawmakers at a hearing when asked directly whether Ukraine has bioweapons. 

"So we are working with the Ukrainians on how they can prevent any of those research materials from falling into the hands of Russian forces should they approach." 

US Senator Marco Rubio noted there were "Russian propaganda" reports claiming the discovery of a plot by Ukrainians to release biological weapons, with co-ordination from Nato. 

Asked by Rubio if a biological or chemical weapon attack were to occur inside Ukraine, whether Russians would be behind it, Nuland asserted: "There is no doubt in my mind, senator." 

"And it is a classic Russian technique to blame on the other guy what they're planning to do themselves." 

On March 6, Moscow's foreign ministry tweeted that Russian forces found evidence that Kyiv was "eradicating traces of the military-biological program in Ukraine," financed by the Pentagon. 

The Atlantic Council, a think tank headquartered in Washington, says the Kremlin was seeking to justify its invasion by pushing a false narrative that Ukraine was developing dirty bombs and biological weapons. 

Fresh fears for Chernobyl 

Systems in place to monitor nuclear material at Chernobyl have stopped transmitting safety data, the international nuclear watchdog has warned. 

"The Director General also indicated that remote data transmission from safeguards monitoring systems installed at the Chernobyl NPP had been lost," the International Atomic Energy Agency (IAEA) said. 

"The Agency is looking into the status of safeguards monitoring systems in other locations in Ukraine and will provide further information soon." 

Russian troops took Chernobyl – the site of the world's worst nuclear disaster in 1986 – on February 24. 

Since then, more than 200 technical personnel and guards have been trapped at the site, with growing fears about their safety and wellbeing. 

Staff are reportedly unable to rotate, with IAEA Director General Rafael Grossi I stressing "the importance of operating staff being able to rest to carry out their important jobs safely and securely". 

There are ongoing concerns for the welfare of the workers, with reports staff have been limiting themselves to one meal per day as they don't know how long they will be trapped. 

The site is also not set up for sleeping, with temporary dormitories created, including makeshift beds on tables and the floor. 

"I'm deeply concerned about the difficult and stressful situation facing staff at the Chernobyl nuclear power plant and the potential risks this entails for nuclear safety. I call on the forces in effective control of the site to urgently facilitate the safe rotation of personnel there," Mr Grossi said. 

Ukraine running low on vital medical supplies 

According to the World Health Organisation, attacks on Ukrainian hospitals, ambulances and other healthcare facilities have increased "rapidly" over the last few days and vital medical supplies are running low. 

The UN agency said it was working to urgently get medical supplies to Ukraine. 

Ukraine is running low on medical items such as oxygen, PPE, blood products, insulin and surgical supplies. 

Russia announces new policy for sale of foreign currency 

Russia's Central Bank has announced a new policy, allowing Russian citizens with foreign currency accounts to withdraw up to US$10,000 until the 9th of September. 

Anything above that amount will have to be withdrawn in rubles at the market rate. 

'Catastrophic': Suffering goes on in encircled Mariupol as evacuation fails 

Corpses lie in the streets of Mariupol. Hungry people break into stores in search of food and melt snow for water. Thousands huddle in basements, trembling at the sound of Russian shells pounding this strategic port city. 

"Why shouldn't I cry?" Goma Janna demanded as she wept by the light of an oil lamp below ground, surrounded by women and children. "I want my home, I want my job. I'm so sad about people and about the city, the children." 

People sit around a lamp in a bomb shelter in Mariupol, Ukraine, Sunday, March 6, 2022. Photo / AP 

A humanitarian crisis is unfolding in this encircled city of 430,000, and Tuesday brought no relief: An attempt to evacuate civilians and deliver badly needed food, water and medicine through a designated safe corridor failed, with Ukrainian officials saying Russian forces had fired on the convoy before it reached the city. 

Nearly two weeks into the invasion, the Russians have advanced deep along Ukraine's coastline in what could establish a land bridge to Crimea, which Moscow seized from Ukraine in 2014. Mariupol, which sits on the Azov Sea, has been surrounded by Russian soldiers for days. 

Mariupol, said Ukrainian Deputy Prime Minister Iryna Vereshchuk, is in a "catastrophic situation." 

People queue up outside McDonald's in Russia 

Images showing people lining up outside McDonald's in Russia on the day the company announced it would stop operating in the country have been shared online. 

Estee Lauder, Shell, Starbucks, Coca-Cola and PepsiCo have also announced they have suspended operations in Russia. 

The boycott by several big global corporations is having a major impact on the country's economy, with the ruble hitting a new record low on Monday. 

Coca-Cola and PepsiCo latest to suspend operations in Russia 

Following similar announcements earlier today from McDonald's and Starbucks, Coca-Cola and PepsiCo have also announced they are suspending operations in Russia. 

In a statement, Coca-Cola said it is "suspending its business in Russia". 

"Our hearts are with the people who are enduring unconscionable effects from these tragic events in Ukraine," the statement continued. 

"We will continue to monitor and assess the situation as circumstances evolve." 

PepsiCo made a similar announcement today as well, saying it will be suspending all capital investments, advertising, and promotional activities in Russia. The company also said it will stop operations in Ukraine to allow associates to seek safety as war escalates in the country. 

Russian warship that attacked Ukraine's Snake Island 'destroyed' 

One of the two Russian warships that attacked Snake Island, a sliver of land in the Black Sea, has been destroyed, according to Ukrainian military sources. 

The Vasily Bykov, a large patrol corvette commissioned in December 2018, appears to have been hit during a firefight in the early hours yesterday. 

Video shared by the Ukrainian navy showed rocket exchange, followed by the sound of two men trying to work out whether they hit the ship. 

"We f***ing hit them", one of the men confirms. 

The second man invokes the Ukrainian soldier's words from when the island was attacked, saying: "Russian warship, go f*** yourself." 

'We will shoot you like rabid dogs for every child killed': Six machine-gun-wielding Ukrainian women take up arms 

A TikTok video shows six Ukrainian women in military gear pledging to "destroy the enemy". 

The Ukrainian women, wielding machine guns, sent a chilling Women's Day message where they vowed to avenge the death of every child killed in the Russian invasion of Ukraine. 

The six women have posted a defiant video on TikTok pledging to kill the enemy and avenge the death of each Ukrainian child. Photo / TikTok 

Wearing combat gear and holding machine guns and assault rifles, with the Ukrainian flag as backdrop, the women pledge to "destroy the enemy on every inch of Ukrainian land". 

"We are women of Ukraine," one of the women says at the start of the video. 

"We have blessed our men to protect our land. We have already taken our children to safety, we join the men and the Ukrainian army," she adds.  
"In every city, village, forest and field. For every child, woman, old man, damaged houses and streets - we will shoot you like rabid dogs," the women pledge. 

"Glory to Ukraine – death to enemies." 

Around two million refugees, mainly women and children, have fled the country in what is the largest humanitarian crisis since WWII. 

'Real threat of nuclear attack', international security expert says 

International security expert David Welch, who is based in Canada, said on the AM Show that the threat of a nuclear attack was real if Putin was feeling irrational, stressed and if he felt like he was losing the battle. 

Putin wanted his troops to operate in Ukraine and didn't want a radiated battlefield so would be aiming elsewhere. 

He told AM he would be stunned if there were a scenario that Russian military planners had even considered where Putin initiated the use of weapons when Russia was not under attack. Russian doctrine was to only use nuclear weapons for self-defence. 

A young girl sings Let It Go while hiding from bombs in Kyiv. Video / Marta Smekhova 

He imagined it would be some kind of demonstration shot or series of demonstration shots. 

"I wouldn't want to be the Russian planner whose job it was to try and pick those. I don't think I would want to pick capital cities in decapitation efforts because I would want to have senior leaders in other countries to talk to and negotiate something down the road." 

He said they would probably aim for a naval base or airfield in Europe or the US and it would be a "reckless act" to only signal seriousness on Putin's part. "And what does he follow up with?" 

Some countries had been attacked in the past and had decided not to respond, he said. 

There had been a lot of prudent restraint from Biden and other leaders of other countries in Putin's earlier nuclear alert, but Welch said the pressure to retaliate if there was an attack on a Western base would be "very very intense" and it would be interesting to know what the conversation would be and if they would retaliate. 

US bans Russian oil 

President Joe Biden announced this morning (NZ time) that the US will ban all Russian oil imports, toughening the toll on Russia's economy in retaliation for its invasion of Ukraine. But he acknowledged it will bring costs to Americans, particularly at the gas pump. 

The action follows pleas by Ukrainian President Volodymyr Zelenskyy to US and Western officials to cut off the imports, which had been a glaring omission in the massive sanctions put in place on Russia over the invasion. Energy exports have kept a steady stream of cash flowing to Russia despite otherwise severe restrictions on its financial sector. 

"We will not be part of subsidising Putin's war," Biden declared, calling the new action a "powerful blow" against Russia's ability to fund the ongoing offensive. 

He warned that Americans will see rising prices, saying, "Defending freedom is going to cost." 

A Ukrainian firefighter walks between at fragments of a downed aircraft seen in Kyiv, Ukraine, on February 25. Photo / AP 

Biden said the US was acting in close consultation with European allies, who are more dependent on Russian energy supplies and who he acknowledged may not be able to join in immediately. The announcement marked the latest Biden attempt at cutting off Russia from much of the global economy and ensuring that the Ukraine invasion is a strategic loss to President Vladimir Putin, even if he manages to seize territory. 

"Ukraine will never be a victory for Putin," Biden said. 

The European Union this week will commit to phasing out its reliance on Russia for energy needs as soon as possible, but filling the void without crippling EU economies will likely take some time. The UK announced that oil and oil products from Russia will be phased out by the end of the year. 

US, Britain ban Russian oil imports 

The US and Britain are banning imports of Russian oil, the latest sanctions intended to punish Moscow for its invasion of Ukraine. 

US President Joe Biden announced the country is "targeting the main artery of Russia's economy" by banning the imports. 

British Business Secretary Kwasi Kwarteng said oil and oil products from Russia would be phased out by the end of the year. 

President Joe Biden announces a ban on Russian oil imports, toughening the toll on Russia's economy in retaliation for its invasion of Ukraine, Tuesday, March 8, 2022. Photo / AP 

He said the transition period "will give the market, businesses and supply chains more than enough time to replace Russian imports", which account for eight per cent of UK demand. 

Kwarteng said the UK would work with its other oil suppliers, including the US, the Netherlands and the Gulf states, to secure extra supplies. 

The bans followed pleas from Ukrainian President Volodymyr Zelenskyy to US and Western officials to cut off the imports, which had been a glaring omission in the massive sanctions put in place on Russia over the invasion. 

On the ground in Ukraine 

Buses carried civilians out of an embattled Ukrainian city on Tuesday along a safe corridor agreed to by the two warring sides, while a parallel effort to relieve the besieged port of Mariupol was thrown into jeopardy by reports of renewed Russian shelling. 

Europe's worst refugee crisis since World War II grew even more severe, with UN officials reporting that two million people have now fled Ukraine. 

Moscow's forces have laid siege to Ukrainian cities and cut off food, water, heat and medicine in a growing humanitarian disaster. But for days, attempts to create corridors to safely evacuate civilians have stumbled amid continuing fighting and objections to the proposed routes. 

A girl sits in the improvised bomb shelter in Mariupol, Ukraine, Monday, March 7, 2022. Photo / AP 

On Tuesday (Ukraine time), a convoy of buses packed with people fleeing the fighting moved along a snowy road from Sumy, a northeastern city of a quarter-million people, according to video from the Ukrainian communications agency. 

Ukrainian Deputy Prime Minister Iryna Vereshchuk said they were headed southwest to the Ukrainian city of Poltava, and included students from India and China. 

Hours before the convoy reached Sumy, overnight strikes killed 21 people there, including two children, Ukrainian authorities said. 

A man carries an elderly woman as people continue to leave Irpin, on the outskirts of Kyiv, Ukraine, Tuesday, March 8, 2022. Photo / AP 

Meanwhile, buses emblazoned with red cross symbols carried water, medicine and food towards the encircled southern port of Mariupol, scene of some of the worst desperation. Vereshchuk said the vehicles would then ferry civilians out of the city of 430,000 people. 

But soon after officials announced that buses were on their way, Ukrainian authorities said they had learned of shelling on the escape route. 

It was unclear whether the supply convoy made it to Mariupol. It appeared unlikely that civilians would be able to board the buses to get out. 

The deputy mayor of Mariupol cast doubt on the evacuations, telling the BBC that Russian forces continued to pound areas where people were trying to gather ahead of being taken out. He said some roads were blocked, while others were mined. 

"So we cannot establish sustainable cease-fire and safety route at the moment,″ Serhiy Orlov said. "So we still have a city in blockade." 

The city is without water, heat, working sewage systems or phone service. Residents have been getting water from streams or by melting snow. Corpses lay in the streets, and authorities planned to start digging mass graves for the dead. 

With the electricity out, many people are relying on their car radios for information, picking up news from stations broadcast from areas controlled by Russian forces or Russian-backed separatists. 

Looting has become widespread for food, clothes and even furniture, with locals referring to the practice as "getting a discount". 

In a video address from an undisclosed location, Zelenskyy said a child had died of dehydration in Mariupol, another sign of the city's desperation. 

McDonald's closes Russian outlets 

McDonald's said it is temporarily closing all of its 850 restaurants in Russia in response to the country's invasion of Ukraine. 

The burger giant said it will continue paying its 62,000 employees in Russia "who have poured their heart and soul into our McDonald's brand". 

But in an open letter to employees, McDonald's president and CEO Chris Kempckinski said closing those stores is the right thing to do for now. 

"Our values mean we cannot ignore the needless human suffering unfolding in Ukraine," Kempczinski said. 

Kempczinski said it's impossible to know when the company will be able to reopen its stores. 

McDonald's has also temporarily closed 100 restaurants in Ukraine and continues to pay those employees. 

- Additional reporting by AP and news.com.au