Moscow has been lashed with multiple warnings to stop its military advance of Ukraine, as grim predictions have been made about its war effort. 

As Ukraine enters its fifth week of invasion, the UN Secretary-General, António Guterres, called on the country to begin peace talks, calling continued military action "unwinnable". 

This comes as a key spokesman for Vladimir Putin refused to quash fears of Russia issuing a nuclear attack. 

In an exclusive interview with CNN, Dmitry Peskov said Russia would consider the use of atomic weapons should they face an "existential threat" from Ukraine. 

The US is currently preparing further sanctions against more than 300 members of Russia's lower house of parliament. The new measures will be implemented as soon as Thursday, according to the Wall Street Journal. 

"We will have additional sanctions measures to announce that will be rolled out in conjunction with our allies on Thursday when the President has the opportunity to speak with them," a White House statement said. 

Russia's invasion of Ukraine is not going well. 

Zelenskyy calls for global rally 

Ukraine President Volodymyr Zelenskyy has today called on people all over the world to take to the streets to protest the war in Ukraine. 

"I ask you to stand against the war! Starting from March 24 – exactly one month after the Russian invasion… From this day and after then," Zelenskyy has said. 

"Show your standing! Come from your offices, your homes, your schools and universities. Come in the name of peace. Come with Ukrainian symbols to support Ukraine, to support freedom, to support life," he added. 

"Come to your squares, your streets. Make yourselves visible and heard. Say that people matter. Freedom matters. Peace matters. Ukraine matters. From March 24. In the downtowns of your cities. All as one together who want to stop the war." 

Putin stuns the world with shock move 

President Vladimir Putin has audaciously stated on live TV that Russia will only accept payments in rubles (Russian currency) for gas deliveries to "unfriendly countries", which include all EU members, after Moscow was hit by unprecedented sanctions over Ukraine. 

It means that these nations will soon have to convert their payments to Russian rubles if they want gas. 

"I have decided to implement a set of measures to transfer payment for our gas supplies to unfriendly countries into Russian rubles," Putin said during a televised government meeting, ordering the changes to be implemented within a week. 

Putin ordered the nations' central bank to develop a mechanism to make ruble payments in a matter of days. 

Russia has earlier named the US, UK and members of the European Union "unfriendly" nations. 

"At the same time, I want to emphasise that Russia will definitely continue to supply natural gas in line with the volumes and prices, pricing mechanisms set forth in the existing contracts," Putin said. 

Gas prices are surging in response to the move — jumping as much as 21 per cent on ICE Endex in Amsterdam overnight. 

Russian troops take big hit 

Nato says between 7000 and 15,000 Russian soldiers have been killed in four weeks of fighting in Ukraine, where the country's defenders have put up stiffer-than-expected resistance and denied Moscow the lightning victory it hoped for. 

A senior Nato military official said the estimate was based on information from Ukrainian officials, what Russia has released — intentionally or not — and intelligence gathered from open sources. The official spoke on condition of anonymity under ground rules set by Nato. 

When Russia unleashed its invasion on February 24, a swift toppling of Ukraine's democratically elected government seemed likely. It has been Europe's biggest offensive since World War II and Russia brandished the prospect of nuclear escalation if the West intervened. 

But with Wednesday marking four full weeks of fighting, Russia is bogged down in a grinding military campaign, with many dead, no immediate end in sight, and its economy crippled by Western sanctions. US President Joe Biden and key allies are meeting in Brussels and Warsaw this week to discuss possible new punitive measures and more military aid to Ukraine. 

Poland expels dozens of Russian diplomats 

Poland's Interior Minister Mariusz Kaminski confirmed the nation had "expelled 45 Russian spies pretending to be diplomats". 

"The internal security agency has drawn up a list of 45 people working in Poland under the cover of diplomatic activities," ABW spokesman Stanislaw Zaryn told reporters, accusing the suspects of targeting Poland. 

The counter-espionage service said the list of suspects had been transferred to the foreign ministry, tweeting that "ABW is requesting that they be expelled from Polish territory". 

The ABW "has detained a Polish national on suspicion of espionage for the Russian secret services," the spokesman added on Twitter. 

"The detainee worked in the archives of Warsaw's registry office," he said. 

"The activity of the suspect posed a threat to both (the) internal and external security of Poland." 

Putin warned as officials claim army is 'static' 

UK's Ministry of Defence has revealed Russia's fighting force in the north is "largely static" and is yet to get into a viable position to take the capital of Kyiv, almost one full month into the current conflict. 

"Russian forces are likely conducting a period of reorganisation before resuming large-scale offensive operations," the latest dossier released on Wednesday read. 

The senior defence official said that while Russia had suffered heavy losses, their reserves were also large. Photo / Getty Images 

Analysts believe the move is part of an attempt to "envelop Ukrainian forces in the east of the country", as the demolition of southern cities, including the "hellscape" in Mariupol, continues. 

It came as German Chancellor Olaf Scholz urged Moscow to "immediately" stop fighting, declaring the campaign has hit a major snag despite continuous attacks on civilian centres. 

"Putin's offensive is stuck despite all the destruction that it is bringing day after day," Scholz said in a speech to the German parliament. 

"But that is just the beginning, many of the toughest consequences will only been seen in the coming weeks," he said, warning the under-fire leader the EU "are constantly creating sanctions". 

Meanwhile, Ukraine's deputy Prime Minister Iryna Vereshchuk said an agreement has been reached between the opposing powers to try to evacuate civilians trapped in Ukrainian towns and cities via nine humanitarian corridors today. 

Russia seizes humanitarian convoy 

Ukrainian President Volodymyr Zelenskyy has accused Russian forces of seizing 15 humanitarian workers on their way to provide essential aid for the decimated city of Mariupol, as evacuations and shelling continue into the four-week long conflict. 

"Sadly, almost all of our efforts are sabotaged by Russian occupants, by [their] shelling or deliberate terror," he said. 

"Today, one of the humanitarian convoys was seized by occupants on an arranged route near Mangush. 

"Employees of the State Emergency Service and bus drivers have been taken captive. We are doing everything to set our people free and unblocked the movement of humanitarian cargo." 

Nearly 100,000 people are reported to be trapped inside the ruins of Mariupol. The besieged port city has faced weeks of bombing and shelling from Russian forces, while being cut off from water, electricity, food and medication. 

The conditions are so poor, they've been described by the Human Rights Watch as a "freezing hellscape riddled with dead bodies and destroyed buildings". 

While Ukraine President Volodymyr Zelenskyy estimates 7026 have been able to escape the city, several attempts to create humanitarian corridors and evacuations have previously been sabotaged by Russian attacks. 

On the President's Tuesday nightly address (local time), Zelenskyy said the remaining residents were living in "inhumane conditions" with Russian troops instilling "deliberate terror" on those attempting to flee. 

Earlier in the day, Zelenskyy issued a grim plea to the Kremlin where he urged Russia to allow civilians to evacuate Mariupol. 

"There is nothing left there. Only ruins," said Zelenskyy in a video-link up with the Italian parliament. 

Reports from Tuesday morning also suggested that Russian soldiers have begun entering the city. 

This comes as the city was rocked by two "super powerful bombs" on Wednesday morning, however the death toll as a result of the attack has yet to be revealed. 

A devastating bombing of a Mariupol theatre on March 16 was believed to have hit a theatre where hundreds of civilians were sheltering in. Photo / Supplied 

Russia refuses to deny use of nuclear weapons 

In a bold declaration, Putin's press secretary refused to quash the potential for nuclear weapons to be used in Russia's assault on Ukraine. 

CNN reports Dmitry Peskov repeatedly denied ruling out the possibility of a nuclear attack in order to achieve Russia's military goals. 

"If it is an existential threat for our country, then it can be," Peskov told CNN's chief international correspondent Christiane Amanpour. 

Peskov doubled down on Russia's goals to demilitarise Ukraine and accused the government of being "nationalist battalions". 

When asked about how Russia was progressing in the conflict, Peskov vaguely hinted Putin "hasn't achieved" his goals to date but said it was "going on strictly in accordance with the plans and the purposes that were established beforehand". 

Watch cruise missiles head for Ukraine 

Footage has been shared of several cruise missiles being launched off the coast of Russia-occupied waters. 

CNN confirmed the geolocation of the footage, which shows projectiles headed towards Ukraine from Sevastopol, the largest city in Crimea. 

Speaking in Russian, a man's voice can be heard saying: "It's clear there's a ship standing out there in the distance. It's firing something, but where, you can't see." 

The video showed missiles being launched from a ship off the coast of Crimea. Photo / Telegram 

Located at the bottom of Ukraine, Russia annexed the Crimean peninsula from Ukrainian rule in 2014. However, the territory is still internationally recognised as being a part of Ukraine. 

'Dangerous new period' in Russian war 

Military analysts fear Russia could change tactics in its war on Ukraine as the nation's military struggle to make inroads on the ground. 

An assessment from the US-based Institute for the Study of War shared fears Russian forces may resort to bombings and bombardments, which could result in higher civilian casualties. 

"If the war in Ukraine settles into a stalemate condition, Russian forces will continue to bomb and bombard Ukrainian cities, devastating them and killing civilians, even as Ukrainian forces impose losses on Russian attackers and conduct counter-attacks of their own," the assessment from March 19 read. 

"The Russians could hope to break Ukrainians' will to continue fighting under such circumstances by demonstrating Kyiv's inability to expel Russian forces or stop their attacks even if the Russians are demonstrably unable to take Ukraine's cities. 

"Ukraine's defeat of the initial Russian campaign may therefore set conditions for a devastating protraction of the conflict and a dangerous new period testing the resolve of Ukraine and the West." 

Examples of this more aggressive strategy has already been seen in Mariupol, where Russian forces have begun shelling the city from the sea, a senior Pentagon official said. 

Up to seven Russian warships have been seen in the Sea of Azov, the Washington Post reported. 

Key Russian ally 'likely' to join war 

One of Russia's key allies – Belarus – could "soon" join the invasion of Ukraine, in claims made by US and Nato officials. 

It's believed Belarus has already begun "preparing the environment to justify" the offensive. 

"Putin needs support. Anything would help," a Nato official told CNN. 

While Belarusian President Alexander Lukashenko is an established ally of Putin, the country has served as a geographical staging ground for Russia's attack. 

Russian forces partially entered Ukraine from Belarus which sits to its north, with Putin also attempting to offer the country as a potential safehaven for Ukrainian refugees, in a move that was admonished by the Ukrainian and international governments. 

Controversially, Lukashenko also accused Western nations, i.e. Nato countries, into pushing Russia into the war. This links back to Putin's initial justification of the invasion for the purposes of the "demilitarisation" of Ukraine. For reference he also called for the "denazification" of the country too, despite the Ukrainian President being Jewish himself. 

"Now there is a lot of talk against the banking sector, gas, oil, SWIFT," he said. 

"It's worse than war. This is pushing Russia into a Third World War. 

"We need to be restrained here so as not to get into trouble. Because nuclear war is the end of everything."