Russia has begun bringing in foreign fighters skilled in urban combat, in a grim sign the Ukraine conflict is about to enter a bloody new phase.

The Wall Street Journal reports Moscow has been recruiting Syrians, some of whom have already arrived in Russia, hoping their expertise can help it take Kyiv.

It comes as Volodymyr Zelensky has accused the West of wanting "us to be slowly killed" as the Ukrainian President again demanded Nato enter the war against Russia.

Russia's invasion of Ukraine, now into its 12th day, has seen more than 1.5 million people flee the country in what the United Nations has called "Europe's fastest growing refugee crisis since World War II".

Hundreds of civilians have been killed and thousands wounded, with hundreds of thousands of mostly women and children pouring into neighbouring countries such as Poland, Romania or Moldova for refuge.

"We repeat every day, 'Close the sky over Ukraine!'" Zelensky said in a video message.

"If you do not do that, if you at least do not give us aircraft for us to be able to protect ourselves, there can be only one conclusion – you also want us to be slowly killed."

His comments came as a furious Ukrainian national guard soldier slammed the US as a "nation of liars" for not doing more to assist against Russia's invasion, including imposing a no-fly zone – which Western leaders including US President Joe Biden have emphatically ruled out as it would lead to "World War III".

"You are afraid to clear our skies because you are afraid of Russia," the soldier told Fox News in Kyiv.

"You are a nation of f***ing liars. We give our nuclear power and our nuclear weapons for your guarantees – your guarantees is nothing."

Moscow recruiting Syrians for urban combat

Moscow is recruiting Syrians skilled in urban combat to fight in Ukraine, US officials have told the Wall Street Journal.

Russia has been operating in Syria since 2015, and in recent days has been recruiting fighters hoping their expertise can help it take Kyiv, according to the report, which adds that some are already in Russia preparing to enter the conflict. Volunteers have reportedly been offered US$200-300 "to go to Ukraine and operate as guards" for six months at a time.

Chechen forces under leader Ramzan Kadyrov, an ally of Vladimir Putin, have already been deployed in the invasion, while foreign fighters are also pouring into the country to fight on the side of Ukraine.

A man opens his arms as he stands near a house destroyed in the Russian artillery shelling, in the village of Horenka close to Kyiv, Ukraine yesterday. Photo / AP

Six hundred missiles fired into Ukraine

Russia has launched an estimated 600 missiles at Ukrainian targets since the war began, a senior defence official has told Fox News and CNN, adding Russia has committed approximately 95 per cent of its amassed combat power inside Ukraine.

The official said the attacks have so far not cut off civilian communications. They added that Ukrainian air space remains contested, noting Ukraine's air and missile defence has so far been effective and remains in use.

Russia says it has destroyed "practically all" of Ukraine's combat-ready aircraft and warned its neighbours including Nato member Romania not to host Kyiv's military aircraft, saying it would drag them into the war.

'Tell Russian mothers' children are dying 

Ukraine's first lady has asked the international media to share the "terrible truth" of how Russian forces are killing children. 

"I appeal to all the unbiased media in the world! Tell this terrible truth – Russian invaders are killing Ukrainian children," Olena Zelenska posted on Instagram below photos of five children killed by Russian attacks, per the NY Post. At least 38 children have died in the conflict so far. 

"Tell it to Russian mothers – let them know what exactly their sons are doing here, in Ukraine," the photo caption read. "Show these photos to Russian women – your husbands, brothers, compatriots are killing Ukrainian children! Let them know that they are personally responsible for the death of every Ukrainian child because they gave their tacit consent to these crimes." 

Putin 'not irrational': Israeli PM

Israeli Prime Minister Naftali Bennett reportedly found Vladimir Putin to be in a rational state of mind during their meeting in Moscow on Saturday, contrary to Western assessments that he may have become unhinged, the Times of Israel reports.

A source close to the PM was quoted by Israel's Channel 13 news as saying the Russian President was "not conspiracy theorising or irrational, nor is he suffering from rage attacks".

Bennett, who afterwards flew to Berlin for talks with German Chancellor Olaf Scholz, was the first Western leader to sit down with Putin since the invasion began. Few details were provided of either meeting. "I went there to assist the dialogue between all of the sides, of course with the blessing and encouragement of all players," he told a weekly cabinet meeting on Saturday.

Ukraine President Volodymyr Zelenskyy said in a video broadcast on Sunday that it was clear Western sanctions weren't deterring Russia. Photo / AP

Plea to strengthen sanctions

As Russian forces increased their shelling, President Volodymyr Zelenskyy appealed to the West to strengthen sanctions.

In a video statement Sunday evening, Zelenskyy heaped criticism on Western leaders for not responding to the Russian Defense Ministry's announcement that it would strike Ukraine's military-industrial complex, while telling employees of these defense plants not to go to work.

"I didn't hear even a single world leader react to this," Zelenskyy said. "The audacity of the aggressor is a clear signal to the West that the sanctions imposed on Russia are not sufficient."

Zelenskyy called for organising a "tribunal" to bring to justice those who order and carry out such crimes.

"Think about the sense of impunity of the occupiers that they can announce such planned atrocities," he said.

The Russian Defense Ministry announced Sunday that its forces intend to strike Ukraine's military-industrial complex with what it said were precision weapons.

"We urge all personnel of Ukrainian defense industry plants … to leave the territory of their enterprises," ministry spokesman Igor Konashenkov said in a statement carried by the state news agency Tass.

Russia detains 4600 at protests

More than 4600 people in cities across Russia were detained at protests on Sunday against Moscow's military operation in Ukraine, a monitoring group says.

A police spokeswoman said 1700 people were detained in Moscow after around 2500 took part in an "unsanctioned protest", while 750 were detained at a smaller rally of around 1500 people in the second largest city of Saint Petersburg, Russian news agencies reported.

OVD-Info, which monitors detentions at opposition protests, put the figure of detainees in 65 towns and cities across Russia at 4644 people. It said police had used electric shockers on protesters, and posted witness photos and videos on Telegram showing riot police beating protesters with batons and demonstrators with blood running down their faces.

Fears of food crisis as wheat shipments halt

With shipments from ports on the Black Sea grinding to a halt as a result of the invasion, wheat prices have soared to record highs, overtaking the food crisis of 2007-08 – sparking fears of worsening inflation and civil unrest.

Russia is the world's largest wheat exporter while Ukraine is the fifth-largest. Together the two countries export about one third of the world's wheat, and are major suppliers for countries including Lebanon and Turkey.

"If farmers in Ukraine don't start planting any time soon there will be huge crisis to food security," Kees Huizinga, a Dutch national who runs a farm in central Ukraine producing wheat, barley and corn, told the Financial Times. "If Ukraine's food production falls in the coming season the wheat price could double or triple."

TikTok and Netflix are suspending most of their services in Russia as the government cracks down on what people and media outlets can say about Russia's war in Ukraine. Photo / AP

Netflix, TikTok block services in Russia

Netflix and TikTok suspended most of their services in Russia on Sunday as the government cracks down on what people and media outlets can say about Russia's war in Ukraine.

TikTok said Russian users of its popular social media app would no longer be able to post new videos or livestreams and they also wouldn't be able to see videos shared from elsewhere in the world.

Netflix said it was suspending its service in Russia but didn't provide additional details.

The actions are likely to further isolate the country and its people after a growing number of multinational businesses have cut off Russia from vital financial services, technology and a variety of consumer products in response to Western economic sanctions and global outrage over the invasion of Ukraine.

Russian President Vladimir Putin on Friday intensified a crackdown on media outlets and individuals who fail to hew to the Kremlin line on Russia's war in Ukraine, blocking Facebook and Twitter and signing into law a bill that criminalises the intentional spreading of what Moscow deems to be "fake" reports.

TikTok is part of the larger Chinese tech company ByteDance.

AmEx suspends operations

American Express announced Sunday it is suspending all operations in Russia and Belarus.

Globally issued American Express cards will no longer work at merchants or ATMs in Russia, the company said in a statement. AmEx cards issued locally in Russia by the country's banks will also no longer work outside of Russia.

The company previously halted its relationships with banks in Russia impacted by the US and international government sanctions, the company said.

People hide from the Russian artillery shelling in a school basement in the village of Horenka close to Kyiv, Ukraine yesterday. Photo / AP

Russians tighten grip on nuclear plant

The International Atomic Energy Agency has said Russian forces are tightening their grip on the Zaporizhzhya nuclear plant, Ukraine's largest, that they seized last week.

The director-general of the agency, Rafael Mariano Grossi, said Sunday Ukrainian staff members are now required to seek approval for any operation, even maintenance, from the Russians, and that they have impeded normal communications by switching off some mobile networks and internet at the site.

Ukraine's regulatory authority said that phone lines, as well as emails and fax, are no longer working. Grossi said he is "extremely concerned about these developments," adding that for the plant to operate safely, "staff must be allowed to carry out their vital duties in stable conditions, without undue external interference or pressure."

People cross an improvised path under a destroyed bridge while fleeing the town of Irpin, near Kyiv on March 6. Photo / AP

Second evacuation attempt fails

A Ukrainian official says a second attempt to evacuate civilians from a southern city under siege for a week has failed due to continued Russian shelling.

Ukrainian military authorities said earlier Sunday that evacuations from the port city of Mariupol were scheduled to begin at noon local time (10am GMT) during an 11-hour ceasefire.

Interior Ministry adviser Anton Gerashchenko said the planned evacuations along designated humanitarian corridors were halted because of an ongoing assault.

He said on Telegram that "there can be no 'green corridors' because only the sick brain of the Russians decides when to start shooting and at whom."

A similar cease-fire planned for Mariupol and the nearby city of Volnovakha collapsed on Saturday, trapping residents under more shelling and aerial bombardment by Russian forces.

A factory and a store burn after having been bombarded in Irpin, in the outskirts of Kyiv, Ukraine yesterday. Photo / AP

Russia warns Ukraine's neighbours

The Russian military has warned Ukraine's neighbouring countries from hosting its warplanes, saying Moscow may consider them a part of the conflict if Ukrainian aircraft fly combat missions from their territory.

Russian Defense Ministry spokesman Igor Konashenkov charged Sunday that some Ukrainian combat planes had redeployed to Romania and other Ukraine neighbours he didn't identify.

Konashenkov warned that if those warplanes attack the Russian forces from the territory of those nations, it "could be considered as those countries' engagement in the military conflict."

No fly zone could spark world war

European Union leader Charles Michel said Sunday closing Ukraine's airspace could spark a world war.

Ukrainian President Volodymyr Zelenskyy has repeatedly called on Nato countries to stop the Russian onslaught on his country by imposing a no-fly zone. Western leaders have refused for fear of triggering a wider war in Europe. Deploying fighter jets over Ukraine could "in current circumstances" be considered as "Nato's entry into the war and therefore risk World War III," Michel said in an interview with the public broadcaster France Inter.

Michel denied that economic sanctions against Russia constitute "a war of the EU or Nato against Russia." Putin has linked the West's economic punishment for his invasion of Ukraine to "declaring war" on Moscow.

Michel said European and American allies imposed sanctions "to create pressure and hurt the (Russian) regime", not the people.

A woman is carried by Ukrainian soldiers along an improvised path while fleeing the town of Irpin, Ukraine yesterday. Photo / AP

364 civilians confirmed dead

The UN human rights office says it has confirmed the deaths of 364 civilians in Ukraine since the Russian invasion began on February 24.

The Geneva-based office said that another 759 civilians had been injured as of midnight Saturday.

The rights office uses strict methodology and only reports casualties it has confirmed.

It says it believes the real figures are considerably higher, "especially in government-controlled territory and especially in recent days." That's because the flow of information has been delayed amid the fighting and many reports still need to be corroborated.

Ukrainian officials have presented far higher numbers.

Vatican sends two cardinals to Ukraine

Pope Francis says he has dispatched two cardinals to Ukraine, a highly unusual move.

The pontiff said Sunday that "the Holy See is willing to do everything to put itself in service for peace." The papal almsgiver, Cardinal Konrad Krajewski, has been dispatched with aid, along with Cardinal Michael Czerny, who is head of the papal office that deals with migration, charity, justice and peace.

Francis did not say where exactly the cardinals had gone, but said they represented him and all Christian people with the message that "war is madness.''

Referring to Ukraine as "that martyred country," Francis called for a cessation of violence, the establishment of humanitarian corridors and a return to negotiations.

"In Ukraine, rivers of blood and tears are flowing. This is not just a military operation, but a war that sows death, destruction and misery,'' he said in his traditional Sunday blessing.

1.5 million refugees leave Ukraine

The head of the United Nations' refugee agency says that more than 1.5 million refugees have crossed from Ukraine into neighboring countries since Russia invaded.

Filippo Grandi, the UN high commissioner for refugees, tweeted on Sunday that it is "the fastest growing refugee crisis in Europe since World War II."

His agency didn't immediately give a more precise update on the refugee figures. Grandi is visiting countries that border Ukraine.

- AP