United Nations Secretary-General Antonio Guterres delivers a speech at the Climate Ambition Summit at the UN headquarters in New York, on Dec. 12, 2020. (Mark Garten/UN Photo/Handout via Xinhua)

"A five-year extension will not only maintain verifiable caps on the world's two largest nuclear arsenals, but it will also provide time to negotiate new nuclear arms control agreements to grapple with our increasingly complex international environment," said a UN spokesman.

UNITED NATIONS, Jan. 22 (Xinhua) -- UN Secretary-General Antonio Guterres on Friday welcomed the U.S. decision to seek a five-year extension of the New START treaty and Russia's positive reaction to the U.S. proposal.

"The secretary-general welcomes the decision by the United States to seek a five-year extension of the New START treaty, as well as the Russian Federation's reiteration that it also seeks a five-year extension," said Stephane Dujarric, spokesman for Guterres.

"A five-year extension will not only maintain verifiable caps on the world's two largest nuclear arsenals, but it will also provide time to negotiate new nuclear arms control agreements to grapple with our increasingly complex international environment," said the spokesman.

Guterres encourages the United States and Russia to work quickly to complete the necessary procedures for New START's extension before the Feb. 5 expiration and move as soon as possible to negotiations on new arms control measures, said Dujarric.

The New Strategic Arms Reduction Treaty, signed in April 2010, limits the number of deployed strategic nuclear warheads to 1,550 and deployed missiles and bombers to 700 for each country. The treaty entered into force on Feb. 5, 2011, and expires on Feb. 5, 2021.

The White House said Thursday that new U.S. President Joe Biden proposed to Russia a five-year extension of the New START treaty. The Kremlin on Friday welcomed Biden's proposal.