Biden calls B9 allies as 'frontline of collective defence' against Moscow

US President Joe Biden has met leaders of NATO's eastern flank to show support for their security after Moscow suspended a landmark nuclear arms control treaty, which he called a "big mistake".

At the opening of the meeting on Wednesday, Biden reaffirmed the US commitment to their security.

"As NATO's eastern flank, you are the frontline of our collective defence," Biden said.

"You know better than anyone what is at stake in this conflict. Not just for Ukraine, but for the freedom of democracies throughout Europe and around the world." He plans to discuss support for Ukraine before he returns to Washington.

Biden arrived in the Polish capital Warsaw late on Monday after a surprise visit to Kiev just days ahead of the anniversary of Russia's military offensive in Ukraine on February 24, 2022.

READ MORE: Putin delivers nuclear warning to West over Ukraine, suspends START pact

Blame game

Amid the highest tension between Russia and the West since the Cold War over three decades ago, Biden addressed thousands in downtown Warsaw on Tuesday and said "autocrats" like Russian President Vladimir Putin must be opposed.

Hours earlier, Putin delivered lengthy remarks laden with criticism of Western powers, blaming them for the war in Ukraine. Biden said the West was never plotting to attack Russia and the war was Putin's choice.

Putin also backed away from the New START arms control treaty - a 2010 agreement that limits the number of Russian and US deployed strategic nuclear warheads - and warned that Moscow could resume nuclear tests.

"It is a big mistake," Biden said of Putin's decision as he headed into the meeting with eastern European allies.

Earlier on Wednesday, Biden met staff from the US Embassy in Warsaw before gathering leaders of the Bucharest Nine, the countries on NATO's eastern flank such as Poland, Bulgaria and Lithuania that joined the Western military alliance after being dominated by Moscow during the Cold War.

Most are among the strongest supporters of military aid to Ukraine, and officials from countries in the group have called for additional resources such as air defence systems.

Lithuanian President Gitanas Nauseda said he wanted greater involvement of the United States in Europe, NATO's eastern flank and more weapons sent to Ukraine.

READ MORE: One year to Russia-Ukraine conflict: How has it impacted the world

Need to build own defence 

"Let's continue building up our own defences. Eastern NATO flank must remain in our focus. No soft spots should be left."

Lithuania, a former Soviet republic on Russia's doorstep, joined NATO in 2004 and plans to host Biden in July for the security alliance's summit.

Not all of the Bucharest Nine have been quite so ready to help Ukraine, notably Hungary, which has pushed back on some EU sanctions on Russia.

Hungarian Foreign Minister Peter Szijjarto urged a ceasefire and peace talks on Ukraine to prevent further escalation of the war into a broader conflict, a line at odds with calls for an outright Ukrainian victory among many of its neighbours.

"Having seen and listened to the speeches by the presidents of the US and Russia yesterday, I think they would have made humanity a much bigger service by talking to each other," Szijjarto told a news conference in Budapest.

READ MORE: UN convenes as Ukraine seeks votes for 'peace' resolution