Tensions have raged for months over the fate of New START, which caps the number of nuclear warheads held by Washington and Moscow and expires on February 5.

"I have a proposal -- which is to extend the current agreement without any pre-conditions at least for one year to have an opportunity to conduct substantial negotiations," Putin said at a meeting of his security council, according to a Kremlin statement.

At the meeting Putin asked Foreign Minister Sergei Lavrov to "formulate our position to try and get at least some sort of coherent answer from (the US) in the nearest future."

But the US national security advisor, Robert O'Brien, said he had already proposed a one-year extension to Russia -- with the condition that both nations freeze warhead work during that period.

"President Putin's response today to extend New START without freezing nuclear warheads is a non-starter," O'Brien said in a statement.

"The United States is serious about arms control that will keep the entire world safe. We hope that Russia will re-evaluate its position before a costly arms race ensues," he said.

Earlier this week the US negotiator, Marshall Billingslea, said that he and his Russian counterpart had reached a "gentlemen's agreement" on an extension that includes a freeze on nuclear work. But Russia likewise said the proposal was unacceptable.

- Relic of 'reset' -

With three weeks to go before US elections in which President Donald Trump is trailing in polls, the administration indicated it would support preserving the treaty for an unspecified period.

Putin said on Friday it would be "extremely sad" if the treaty, which was successful in containing an arms race, expired.

The agreement was signed in 2010 at the peak of hopes for a "reset" in relations between Russia and the United States, spearheaded by US president Barack Obama and then Russian counterpart Dmitry Medvedev.

But tensions rapidly built up again once Putin returned to the presidency from 2012.

Lavrov said Moscow favoured extending the current treaty for another five years without any conditions but was also ready to work out a new agreement with the Americans.

He said Moscow had handed over to Washington some "concrete proposals".

In response, Russia's top diplomat said, the United States came up with a number of proposals described as pre-conditions necessary to extend New START.

These "numerous" proposals lie both outside the framework of the agreement and "outside our responsibility," Lavrov said, without giving further details.

- 'Chance to save treaty' -

Together with the Cold War-era Intermediate-Range Nuclear Forces (INF) treaty, New START was considered a centrepiece of superpower arms control.

In 2019, the United States withdrew from the INF, which limited missiles that could hit European cities, after saying that Moscow was in violation.

Trump's administration has been insisting without success that its new nemesis China enter the New START treaty, which has limited the United States and Russia to 1,550 deployed nuclear warheads each.

"What Americans have been offering is a radically new agreement," Vasily Kashin, a military expert at Moscow's Higher School of Economics, told AFP.

Besides the inclusion of China, Washington's insistence to have tactical nuclear weapons and new weapons covered by New START or its replacement has been another issue in the talks, said Kashin.

Russia's arsenal of short-range tactical nuclear weapons is believed to be bigger and more varied than that of the United States so it would be a "one-sided concession" on Moscow's part, he said.

In the current conditions extending the treaty for a year would be "ideal", he said. "It is a chance to preserve it."

Dmitry Trenin, head of the Moscow Carnegie Center, tweeted that Putin did not want to make concessions "just to help Trump's campaign," noting that Democratic challenger Joe Biden supports extending the treaty.