Ukraine allies vow to strengthen defenses as UN chief slams invasion

US president Joe Biden met NATO and European leaders in Warsaw on Wednesday, with the allies vowing to strengthen defences "from the Baltic to the Black Sea", as the UN secretary-general condemned Russia's invasion.

Biden attended a meeting with NATO chief Jens Stoltenberg and the heads of eastern European countries in a bid to shore up support for Kyiv nearly a year after Russian forces rolled into Ukraine.

The leaders of Bulgaria, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania and Slovakia joined the talks amid widespread concern in their countries that the conflict could spill over.

In a statement after the meeting, the leaders vowed to further "reinforce our deterrence and defense posture across the entire Eastern flank from the Baltic to the Black Sea."

Stoltenberg urged allies to step up support for Ukraine, saying: "we cannot allow Russia to continue to chip away at European security".

The UN General Assembly met for a special session Wednesday that was to debate a motion backed by Kyiv and its allies calling for a "just and lasting peace."

UN secretary-general Antonio Guterres told the session that the invasion of Ukraine is "an affront to our collective conscience, while Moscow's UN ambassador took aim at the West, saying it is "ready to plunge the entire world into the abyss of war" to defeat Russia.

In Moscow, president Vladimir Putin attended a patriotic rally, telling a crowd of tens of thousands that Russia was fighting "for our historical lands, for our people".

Earlier, Putin held talks with China's top diplomat Wang Yi, who was visiting Moscow after Washington and NATO voiced concern that China could be preparing to supply Russia with weapons.

"We will not be overwhelmed by threats and pressure from third parties," Wang said.

A readout following the meeting published by Chinese state news agency Xinhua quoted Wang saying China was willing to "deepen political trust" and "strengthen strategic coordination" with Russia.

China would "uphold an objective and fair position and play a constructive role in solving the crisis through political means", it said.

On Tuesday, Putin announced the suspension of Moscow's participation in the New START nuclear arms reduction treaty and promised to press on with the campaign in Ukraine, during a state of the nation address.

Speaking in Warsaw, Biden said the decision on the treaty was a "big mistake".

Russian lawmakers on Wednesday approved the suspension of the 2010 deal -- the last remaining nuclear arms control treaty between the world's two main nuclear powers.

Putin's announcement on New START met with international condemnation, though Russia's foreign ministry later said Moscow would continue to comply with the treaty's restrictions in a "responsible approach".

Beijing has sought to position itself as a neutral party in the war, while maintaining close ties with strategic ally Russia.

It has said it is "deeply concerned" and that the conflict is "intensifying and even getting out of control".

Wang is on the last stop of a European tour during which he also met Ukraine's Foreign Minister Dmytro Kuleba.

Moscow said Wednesday that Beijing had presented its views on paths towards a "political settlement" in Ukraine following Wang's visit.

"The Chinese partners briefed us on their views on the root causes of the Ukrainian crisis as well as approaches to its political settlement. There was no talk of any separate (peace) 'plan'," the Russian foreign ministry said.

At the start of the meeting with Wang, Putin said cooperation between Russia and China was "very important to stabilise the international situation".

When the Kremlin launched its invasion of Ukraine, it was designed to be a rapid conquest leading to capitulation and the installation of a pro-Russian regime.

Since then, Russia has been forced to give up ground but has kept up a barrage of drone and missile attacks, while the military and civilian toll has spiralled.

Various Western sources estimate the conflict has caused 150,000 casualties on each side.

Moscow's relentless struggle to capture the city of Bakhmut has also exposed tensions between the Russian military and the Wagner mercenary group.

The group's head, Yevgeny Prigozhin, on Wednesday urged Russians to pressure the country's regular army into sharing ammunition with his fighters in Ukraine.

The 61-year-old Putin ally has been involved in a bitter power struggle with the defence ministry for months as his forces spearhead the assault for towns in eastern Ukraine.