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Moscow said on Monday that Russian officials had begun talks with their United States counterparts on a possible extension of a key nuclear weapons agreement.

The "practical" work on prolonging the New Strategic Arms Reduction Treaty, better known as New START, has started, said Maria Zakharova, a spokeswoman for the Foreign Ministry said.

The secretary of Russia's Security Council, Nikolai Patrushev, had discussed the issue in a phone call with US National Security Adviser Jake Sullivan, Zakharova confirmed.

The arms control treaty, which is due to expire on Feb 5 and was signed in 2010, limits the US and Russia to deploying no more than 1,550 strategic nuclear warheads each. Russia has proposed either an extension to the pact or a new agreement on the limitation of strategic offensive arms, which, the government said, was rejected by the US administration of then-president Donald Trump.

Russia had offered a five-year extension without further conditions. But Trump panned the New START as "another bad deal" that his predecessor Barack Obama had signed, and said he could renegotiate a better one.

US President Joe Biden on Monday said extending the nuclear arms treaty has to be prioritized.

"I find we can both operate in mutual self-interest of our countries as a New START agreement and make it clear to Russia that we are, we are very concerned about their behavior," Biden told reporters at the White House.

NATO welcomes gestures

The gestures from both sides were welcomed by NATO Secretary-General Jens Stoltenberg.

"We should not end up in a situation where we have no limitation whatsoever on nuclear warheads," Stoltenberg said.

"I don't see the treaty's extension as the end, but the beginning of an effort to further strengthen international nuclear arms control," he said in a statement.

The Kremlin said it remained committed to extending the New START. Kremlin spokesman Dmitry Peskov said Russia welcomes efforts promised by the Biden administration to reach an agreement. He hailed the US political willingness on this matter but the outcome would depend on the details of this initiative that were yet to be analyzed.

He stressed that "it is of great importance to respect each other's concerns and take into account Russia's well-known position on the issue".

Russia's permanent representative to international organizations in Vienna, Mikhail Ulyanov, said: "The extension of the New START will give Russia and the US time to consider additional measures to enhance strategic stability."

Former Soviet leader Mikhail Gorbachev, who formalized the Intermediate-Range Nuclear Forces Treaty with then-US president Ronald Reagan in 1987, also called on Moscow and Washington to extend the New START and work together to agree on further cuts to the countries' nuclear stockpiles.

Agencies contributed to this story.