By Nandita Bose and Alan Charlish
WARSAW (Reuters) -U.S. President Joe Biden vowed on Wednesday that "we will defend every inch of NATO" to reassure allies on Europe's eastern flank and described Russia's suspension of a landmark nuclear arms control treaty as a "big mistake".
Biden spoke during talks with eastern European NATO allies in the Polish capital Warsaw two days after a surprise visit to Kyiv, ahead of the first anniversary of Russia's invasion of Ukraine on Feb. 24, 2022.
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 invasion 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 U.S. deployed strategic nuclear warheads - and warned that Moscow could resume nuclear tests.
"It is a big mistake," Biden said of Putin's decision before his session with eastern European allies known as the Bucharest Nine.
"The commitment of the United States to NATO ... is absolutely clear. Article 5 is a sacred commitment the United States has made. We will defend literally every inch of NATO, every inch of NATO," he said.
Article 5 stipulates that an attack on any one member of NATO is treated as an attack on all, requiring a joint response.
Earlier in the day Biden met staff from the U.S. Embassy in Warsaw before gathering leaders of the Bucharest Nine - states such as Poland, Bulgaria and Lithuania that joined the Western military bloc after being dominated by Moscow while under Communist rule 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.
At the meeting, Biden reaffirmed Washington's commitment to their security.
"As NATO's eastern flank, you are the front line of our collective defence. 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."
The Kremlin says it regards NATO, which could soon expand to include Sweden and Finland, as an existential threat to Russia.
In a joint statement after the meeting, the Bucharest Nine said they were committed to increasing NATO's military presence on their territories to deter Moscow. "Russia is the most significant and direct threat to allied security," it said.
The declaration was also signed by Hungary, which has pushed back on some EU sanctions on Russia and along with Turkey is the only NATO member still to ratify the accession applications of Sweden and Finland.
Before Wednesday's meeting, Hungarian Foreign Minister Peter Szijjarto called for a ceasefire and peace talks on Ukraine to prevent further escalation into a broader conflict - a line at odds with calls among many of its neighbours for an outright Ukrainian victory.
"Having seen and listened to the speeches by the presidents of the U.S. 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.
On Wednesday, the Bucharest Nine - including Hungary - reiterated their support for Ukraine.
"Ukraine is exercising its legitimate right to defend itself against the Russian aggression to regain full control of its territory," a statement said. "We will continue to support Ukraine's efforts to this end, as long as necessary."
A White House statement about the talks said the United States and the Bucharest Nine "reaffirmed their unwavering support for Ukraine and underscored their shared commitment to stand with the Ukrainian people for as long as it takes."
It said the leaders looked forward to further strengthening unity and collective defense at a NATO summit in Vilnius in July.
(Reporting by Nandita Bose, Alan Charlish, Pawel Florkiewicz, Anna Koper and Andrius Sytas in Warsaw, Robert Muller and Jason Hovet in Prague, Gergely Szakacs in Budapest; Writing by Niklas Pollard, Gwladys Fouche, Trevor Hunnicutt and Steve Holland; Editing by Raissa Kasolowsky, Mark Heinrich and Alistair Bell)