Russia is suspending its last remaining arms control treaty with the US, President Vladimir Putin said on Tuesday in a state-of-the-nation speech days before the anniversary of the invasion of Ukraine.
Mr Putin blamed the West for the war as he threw the New START treaty into doubt.
His remarks came hours before a speech by US President Joe Biden in Poland, where he rallied for Ukraine after his surprise visit to Kyiv on Monday.
Mr Biden framed the war as a “test for the ages” for the US and its allies in which they had shown their strength, unity and commitment to sovereignty and freedom.
“One year ago, the world was bracing for the fall of Kyiv,” he told a crowd in Warsaw.
“Well I’ve just come from a visit to Kyiv and I can report: Kyiv stands strong. Kyiv stands proud. It stands tall. And most important, it stands free.”
Mr Biden said Mr Putin had miscalculated when he launched the invasion.
“When President Putin ordered his tanks to roll into Ukraine, he thought we would roll over. He was wrong. The Ukrainian people are too brave,” he said.
“America, Europe, a coalition of nations from the Atlantic to the Pacific — we were too unified. Democracy was too strong.”
Aides said the speech was “vintage Joe Biden” and was designed to challenge Mr Putin's narrative about the conflict.
Mr Biden spoke after a meeting with Polish President Andrzej Duda, in which they discussed military, economic and humanitarian assistance from Ukraine's allies.
Western diplomats reacted with concern to the demise of New START, which was signed in 2010 and was to run until 2026.
It is the last remnant of the arms control system developed during the Cold War, and limits each side to 700 long-range missiles and bombers.
“More nuclear weapons and less arms control makes the world more dangerous,” Nato Secretary General Jens Stoltenberg said at a news conference held at Nato headquarters in Brussels.
In Britain, a Downing Street spokesman said the government “will not waver” in its support for Ukraine.
“Nearly one year on, the West's resolve has only been strengthened and Ukraine continues to demonstrate its ability to defend its sovereignty,” the spokesman said.
Mr Putin said Russia would suspend its participation in New START but not pull out completely.
He said move had been forced on Russia, claiming the US was ready to resume nuclear weapons testing — a step neither side has taken since the 1990s.
“If the US conducts tests, then we will. No one should have dangerous illusions that global strategic parity can be destroyed,” he said.
Mr Putin accused the US and its allies of making Ukraine a hostage and using it to menace Russia.
He said Moscow would “carefully and systematically” continue the war as the sides scrap for territory in eastern Ukraine.
“The responsibility for fuelling the Ukrainian conflict, for its escalation, for the number of victims … lies completely with western elites,” Mr Putin said.
“The elites of the West do not hide their purpose. But they also cannot fail to realise that it is impossible to defeat Russia on the battlefield.”
US National Security Adviser Jake Sullivan rejected the Kremlin narrative as a pretext for a “war of choice” against Russia's ex-Soviet neighbour.
“Putin chose to fight it. He could have chosen not to. And he can choose even now to end it, to go home,” he said.
“And nobody is attacking Russia. There's a kind of absurdity in the notion that Russia was under some form of military threat from Ukraine or anyone else.”