An extension of the New Strategic Arms Reduction Treaty "makes the United States, U.S. allies and partners, and the world safer," Secretary of State Antony Blinken said in a statement, adding, "An unconstrained nuclear competition would endanger us all."

The Russian Foreign Ministry said that the two countries exchanged related diplomatic notes on Wednesday and the agreement to extend the New START entered into force the same day.

"Thus the treaty will remain in effect exactly as it had been signed, without any amendments or additions, until Feb. 5, 2026," the ministry said in a statement, emphasizing that the extension comes without any preconditions as Moscow had been insisting.

Blinken said the United States will use the time provided by the extension to work with Russia toward addressing "all of its nuclear weapons" beyond those affected in the New START, and that it will pursue "arms control to reduce the dangers from China's modern and growing nuclear arsenal."

The New START limits each side to no more than 1,550 deployed nuclear warheads and no more than 800 deployed and non-deployed intercontinental ballistic missile launchers, submarine-launched ballistic missile launchers and heavy bombers equipped for nuclear armaments.

The pact, which entered into force in February 2011 for a duration of 10 years, says that the parties may agree to extend it for a period of no longer than five years.

The latest announcements came just ahead of the treaty's scheduled expiration on Friday. U.S. President Joe Biden and Russian President Vladimir Putin had earlier agreed on the extension during their first phone talks after Biden took office on Jan. 20.

The treaty has become the only arms control accord between the world's two nuclear superpowers, after the previous administration of U.S. President Donald Trump withdrew the country from the Intermediate-Range Nuclear Forces Treaty, a 1987 pact with Russia, citing violations by Moscow.

Although the Trump administration had been eager to pursue an arms control framework that would also involve China, Beijing showed no interest in coming to the table.

The Trump administration proposed a conditional one-year New START extension, but the two countries failed to reach an agreement before the end of his presidency.