Russia has warned the Ukraine conflict risks escalating into a third world war and accused Kyiv of playing at peace talks a day after visiting US officials said Ukrainian forces could beat back Moscow's invasion.
The conflict has triggered an outburst of support from Western nations that has seen weapons pour into Ukraine to help them wage war against Russian troops.
Speaking to Russian news agencies, Russian Foreign Minister Sergei Lavrov criticised Kyiv's approach to floundering peace talks, saying the risk of a World War Three "is serious".
"It is real, you can't underestimate it," Mr Lavrov said.
While he said talks with Kyiv would continue, Mr Lavrov accused Ukrainian President Volodymyr Zelenskyy of "pretending" to negotiate, adding: "You'll find a thousand contradictions."
For months, Mr Zelenskyy has been asking Ukraine's western allies for heavy weapons — including artillery and fighter jets — vowing his forces could turn the tide of the war with more firepower.
The calls appear to be resonating now, with a host of pledging to provide a range of heavy weapons and equipment, despite protests from Moscow.
"The first step in winning is believing that you can win," Pentagon chief Lloyd Austin told a group of journalists after he and the United States Secretary of State Antony Blinken met Mr Zelensky in Kyiv.
"We believe that we can win — they can win — if they have the right equipment, the right support."
The meeting between the two sides was "very productive and detailed", according to a Pentagon spokesman, adding that Mr Zelenskyy was also briefed on a security summit in Germany on Tuesday among Western allies.
After the talks, Mr Austin said the United States hoped the Russian military would be exhausted in Ukraine.
"We want to see Russia weakened to the degree that it can't do the kinds of things that it has done in invading Ukraine," said Mr Austin.
The highly sensitive US trip by two of President Joe Biden's top cabinet members came as fighting continued across Ukraine, casting a long shadow over Easter celebrations in the largely Orthodox country.
Volodymyr Zelenskyy hails resistance
"Thanks to the courage, the wisdom of our defenders, thanks to the courage of all Ukrainians — our state is a true symbol of the struggle for freedom," Mr Zelenskyy said in his evening address vowing victory.
Following a weekend full of fighting, at least five people were killed and another 18 injured on Monday after a Russia rocket attack targeted railway infrastructure in the central Ukraine region of Vinnytsia.
On Monday, the governor of a Russian region bordering Ukraine accused Kyiv of bombing one of its villages, injuring two civilians and damaging several houses.
"A village was targeted... It is already clear that there are injured civilians," Belgorod region governor Vyacheslav Gladkov wrote on Telegram.
Russia in recent weeks has accused Ukrainian forces of striking targets on Russian soil, including two villages in Belgorod and another in the region of Bryansk.
A distant view of the premises of Azovstal Iron and Steel Works in the embattled city of Mariupol. Source: AAP / TASS/Sipa USA
The United Kingdom's Defence Secretary Ben Wallace announced on Monday that Britain would send Ukraine armoured vehicles able to fire missiles against Russian warplanes.
"These Stormer vehicles will give Ukraine forces enhanced short-range anti-air capabilities both day and night," he said.
The US has been a leading donor of finance and weaponry to Ukraine, and a key sponsor of sanctions targeting Russia.
But it had not previously sent top officials to Kyiv. Several European leaders have already travelled there to underscore their support.
"Many countries are going to come forward and provide additional munitions and howitzers. So we're going to push as hard as we can, as quickly as we can, to get them what they need," Austin said.
Mr Blinken and Mr Austin also said US diplomats would begin a gradual return to Ukraine this week and announced $700 million (A$975 million) in additional military aid.
Supply lines hit
Forty German diplomats will meanwhile be heading home from Russia after Moscow announced their expulsion, following Berlin's decision to kick out 40 Russian diplomats earlier this month.
From The Hague, the International Criminal Court's chief prosecutor is to join a European Union investigations team to probe "alleged core international crimes committed in Ukraine", officials said.
Russia's air force targeted 82 Ukrainian military sites, including four command posts and two fuel depots, and the army fired high-precision missiles at 27 targets in their latest attacks, the Russian defence ministry said on Monday.
The Ukrainian defence ministry said Russia was continuing to hit infrastructure and supply lines bringing military assistance from Ukraine's partners.
Ukraine's second city Kharkiv remains partially surrounded and Moscow's forces are regrouping in the south, but a Russian attempt to break through towards Zaporizhzhia in the east failed, the ministry added.
Russia on Monday accused Kyiv of preventing civilians trapped with Ukrainian soldiers in Mariupol's Azovstal steelworks from leaving the besieged industrial centre despite a ceasefire announcement.
The defence ministry had said it would allow a civilian evacuation from Mariupol's sprawling steel plant, which has been sheltering the remaining Ukrainian resistance in the southeastern port city.
But the Russian army on Monday evening said no one used the proposed humanitarian corridor.
A video posted by the far-right Azov Regiment, whose fighters are based in Azovstal, showed war-weary women and children sheltering in the plant's underground bunkers, pleading for relief.
"There are 600 people here. No water, no food. What are we going to do here? How long will we stay here?" asked one woman.
"We haven't been out for two months now. I don't even know what the weather is like there. It feels like it's still 28 February," said another woman.
Mariupol, which the Kremlin claims to have "liberated", is pivotal to Russia's war plans to forge a land bridge to Russian-occupied Crimea — and possibly beyond, as far as Moldova.
