Western leaders piled on military and humanitarian aid for Ukraine on Thursday with United States President Joe Biden calling Russian leader Vladimir Putin a "brute" and Britain denouncing Moscow's invasion of its neighbour as "barbarism".
At an unprecedented triple summit in Brussels, transatlantic alliance NATO, G7 rich nations and European leaders addressed the continent's worst conflict since the 1990s Balkans wars.
NATO announced new battle groups for four nations in East Europe, while Washington and London increased aid and expanded sanctions to new targets, including a woman London said was the stepdaughter of Russia's foreign minister.
"This single most important thing is for us to stay unified and the world continue to focus on what a brute this guy is and all the innocent people's lives that are being lost and ruined," Mr Biden told reporters in Brussels.
"Vladimir Putin has already crossed the red line into barbarism," added British Prime Minister Boris Johnson, saying the tougher the sanctions the sooner war would end.
The European Union was set to unveil steps to wean itself off Russian energy, something likely to drive up fuel costs even further around the continent. Moscow supplies 40 per cent of the European Union's collective gas needs and more than a quarter of its oil imports.
Still, the measures stopped short of President Volodymyr Zelenskyy's calls for a full boycott of Russian energy and a no-fly zone over Ukraine where Moscow's bombs are wreaking havoc.
Responding to Thursday's show of unity in Brussels, Moscow said the West had itself to blame for the war by arming the "Kyiv regime".
The invasion unleashed on 24 February by Russian leader Vladimir Putin has killed thousands of people, sent 3.6 million abroad, smashed cities, and driven more than half of Ukraine's children from their homes according to the United Nations.
US making plans in case Russia uses chemical, nuclear weapons
The White House has set up a team of experts to plan how the US could respond should Russia use weapons of mass destruction — chemical, biological or nuclear — during its invasion of Ukraine, senior administration officials said on Thursday.
Russia has repeatedly raised the prospect of using nuclear weapons as it struggles to overcome Ukraine's military during the month-old war that the Russian government calls a "special operation." This week, the Kremlin said such weapons would only be used in the case of an "existential threat."
A Ukrainian serviceman stands guard near a burning warehouse hit by a Russian shell in the suburbs of Kyiv on 24 March, 2022. Source: Getty, AFP / Fadel Senna
Mr Biden said on Thursday that if Russia were to use chemical weapons in its invasion of Ukraine, the United States would respond.
"We would respond, we would respond if he uses it. The nature of the response would depend on the nature of the use," Mr Biden said at a news conference in Brussels.
The White House National Security Council sent an internal memo to agencies on 28 February to create a strategy group to examine major geopolitical shifts that are occurring as a result of Russia's invasion of Ukraine, officials said. A second group, known internally as the "Tiger Team," is looking at what the next three months look like.
The strategy group is working "to monitor and mitigate risks, while considering how to advance and defend US interests," one US official said.
Russia, Ukraine exchange prisoners
Russia and Ukraine have exchanged prisoners, Kyiv and Moscow confirmed on Thursday, in what Ukraine said was the first swap of soldiers since Moscow ordered troops into Ukraine one month ago.
"Following an order from President Volodymyr Zelenskyy, the first fully-fledged exchange of prisoners of war has taken place," Ukrainian Vice Prime Minister Iryna Vereshchuk wrote on Facebook.
"In exchange for 10 captured occupiers we rescued 10 of our servicemen," she said, referring to Russian and Ukrainian troops.
Ms Vereshchuk also said that 11 Russian civilian seamen rescued near the Black Sea port city of Odesa were exchanged for 19 Ukrainian civilian ship crew members held by Moscow.
"I confirm the information regarding the exchange of 10 Russian servicemen detained on Ukrainian territory for 10 Ukrainian servicemen. And there was also an exchange of Russian civilian sailors for Ukrainian civilian sailors", said Russian human rights ombudsman Tatiana Moskalkova.
Refugees fleeing the war in Ukraine stand in a tent after crossing the border by ferry at the Isaccea-Orlivka border crossing in Romania, on Thursday, 24 March, 2022. Source: AAP, AP / Andreea Alexandru
Ms Moskalkova said nine Russian prisoners were exchanged for the mayor of Melitopol, a city in southeastern Ukraine captured by the Russian army.
Ms Vereshchuk on Wednesday confirmed the Melitopol swap but denied any others had taken place.
'Turned to dust'
"A beautiful Mariupol used to be and suddenly it was turned into dust," lamented 83-year-old Raisa Kairat in the besieged southern port that has become a wasteland under bombardment.
In Mariupol, which lies between Russian-annexed Crimea and eastern areas held by Russian-backed separatists, thousands are in basements with scant water, food, medicine or power.
In one part captured by Russian troops, a patch of grass between blasted buildings has become a makeshift graveyard. Freshly-dug mounds are marked with plastic flowers and crosses made from broken window frames.
Explosions sound in the background.
A man walks past the wreckage of a bus in Mariupol, Ukraine, on 23 March, 2022. Source: AAP / TASS/Sipa USA
In a month of fighting, Ukraine has fended off what many analysts had anticipated would be a quick Russian victory.
So far, Moscow has failed to capture any major city. Its armoured columns have barely moved in weeks, stalled at the gates of the capital Kyiv and besieging cities in the east.
They have taken heavy casualties and are low on supplies. Ukrainian officials say they are now shifting onto the offensive and have pushed back Russian forces, including north of Kyiv.
Ukraine said its forces had destroyed the Russian landing ship the "Orsk" at the Russian-occupied port of Berdyansk.
Video footage, which Reuters confirmed was from Berdyansk, showed smoke rising from a blaze at a dock and the flash of an explosion. Russian officials did not immediately respond to requests for comment.
As Biden rallied allies on his first trip abroad since the war began, Washington announced $1 billion (A$1.3 billion) more humanitarian aid for Ukraine and an offer to take in 100,000 refugees. Biden said Russia should be expelled from the G20 group of major economies.
The Kremlin accuses NATO of an "hysterical and inadequate" understanding of events in Ukraine, a former Soviet Republic linked since the 9th century when Kyiv became the capital of the ancient state of Rus. Putin says NATO's eastern expansion threatened Russia's security and divided it from Ukraine.
Russia isolated again at UN
Ukraine's armed forces chief of staff said on Thursday that Russia was still trying to resume offensives to capture the cities of Kyiv, Chernihiv, Sumy, Kharkiv and Mariupol.
Chechen leader Ramzan Kadyrov, a Putin ally, posted on social media that Chechen fighters had captured the main administrative building in Mariupol and raised their flag there. His account could not be confirmed independently.
Satellite photographs from commercial firm Maxar showed massive destruction of what was once a city of 400,000 people, with apartment buildings in flames.
Journalists have not been able to report from the Ukrainian-held part of Mariupol for 10 days, during which time Ukraine says Russia has bombed a theatre and an art school used as shelters, burying hundreds alive.
Ukrainian officials accused Russia on Thursday of having forcibly deported 15,000 people from the city to Russia.
Moscow denies this.
In the Russian-held part of the city, trucks arrived with food supplies in boxes bearing the "Z" symbol of what Russia calls its "special operation". Hundreds of people, many elderly, emerged from ruins, queuing mostly in silence as men in Russian emergencies ministry uniforms distributed boxes.
Angelina, a young mother-of-two, said she had received bread, nappies and baby food. "It's difficult to leave by bus now. We hope the number of people trying to get out will go down and it will get easier for us to leave," she said.
Almost three-quarters of the UN General Assembly demanded aid access in Ukraine and criticized Russia for the "dire" humanitarian situation - the second time the body has overwhelmingly isolated Moscow over the invasion.
