Russia's decision to suspend the New Start nuclear arms treaty has been criticized as a major error by US Vice President Joe Biden.
In his yearly address to the nation on Tuesday, President Vladimir Putin made the announcement.
The 2010 agreement limits the number of nuclear warheads that the US and Russia both possess and grants each country the authority to inspect the other's arsenal.
Mr. Biden made his remarks as he met in Poland with a significant number of NATO allies.
Nearly a year after it began, the Bucharest Nine, a group of eastern European nations, reiterated their opposition to Russia's invasion of Ukraine.
Both houses of the Russian parliament formally approved Putin's decision to halt participation in the nuclear agreement on Wednesday.
But later, the Russian foreign ministry declared that Moscow would uphold the New Start treaty's limitations in a "responsible manner.".
Russia's lower house was informed by a senior military official that the nation would continue to abide by the limitations placed on nuclear delivery systems, which include missiles and strategic bombers.
The New Start treaty, which was signed in 2010 by two presidents at the time—Barack Obama and Dmitry Medvedev—was intended to stop nuclear war. It gives each nation the authority to inspect the other and restricts the total number of strategic nuclear warheads that can be deployed by both sides.
The agreement went into effect in 2011 and was renewed ten years later, despite the Covid pandemic disrupting the weapons inspections.
1,550 long-range nuclear warheads are the maximum allowed for each side, which is fewer than under the previous Start agreement.
The two former Cold War adversaries jointly control nearly all of the world's nuclear weapons. Despite hostile rhetoric on both sides during the Ukraine war, Russia had previously stated that it wanted to keep the treaty in place.
Speaking before the meeting with the Bucharest Nine leaders, who make up Nato's eastern flank, Mr. Biden emphasized the US commitment to the military alliance and called the suspension of New Start a "big mistake.".
"The United States has made a sacred commitment with Article 5.". We will essentially defend every square inch of NATO, he declared. According to Article 5, any attack on a member state is considered an attack on all of them and calls for a coordinated response.
He stated that the leaders present were the "front line of our collective defense" during the meeting. Following the meeting, the group issued a joint statement in which they expressed their commitment to bolstering NATO's military presence on their respective soils.
Russia claims that NATO, whose membership could soon include Sweden and Finland, poses an existential threat.
At a rally in Moscow to commemorate a year of the conflict, Mr. Putin claimed that Russia was fighting in Ukraine for its "historical" lands.
"A battle is ongoing right now, for our historical lands, for our people," he said, citing the country's top military leadership.
In a meeting with Wang Yi, China's top diplomat, earlier in the year in Moscow, he stated that Beijing's cooperation was "very important to stabilize the international situation.".
Beijing is prepared to deepen its partnership with Moscow, according to Mr. Wang, and pressure from other nations won't have an impact on their relationship.