By Dmitry Antonov and Andrew Osborn

MOSCOW (Reuters) - Russia warned on Monday that the outlook for extending the last remaining pillar of nuclear arms control between Moscow and Washington, the world's two biggest nuclear powers, did not look promising and that the situation appeared to be deadlocked.

The New Strategic Arms Reduction Treaty, or New START, which caps the number of strategic nuclear warheads that the United States and Russia can deploy, and the deployment of land- and submarine-based missiles and bombers to deliver them, is due to run out in less than a year - on February 5, 2026.

U.S. President Donald Trump, during his first presidential term, withdrew the U.S. from another important treaty - the Intermediate-Range Nuclear Forces (INF) Treaty - and the New START agreement is now the only pact remaining.

Deputy Foreign Minister Sergei Ryabkov, who oversees U.S. relations and arms control, told a news briefing in Moscow on Monday that the prospects for talks on amending and extending the agreement looked bleak for now.

"As for our dialogue in the field of (nuclear) strategic stability and the post-New START situation, the situation does not look very promising," said Ryabkov.

"On February 5, 2026, the pact expires and after this it will not exist."

Trump in January said he wanted to work towards cutting nuclear arms, adding that he thought Russia and China might support reducing their own weapons capabilities.

"We'd like to see denuclearization ... and I will tell you President Putin really liked the idea of cutting way back on nuclear. And I think the rest of the world, we would have gotten them to follow, and China would have come along too," Trump said.

The Kremlin, commenting on Trump's remarks, said at the time that Russian President Vladimir Putin had made clear he wanted to restart nuclear arms cuts talks as soon as possible.

But Ryabkov said that while the U.S. wanted three-way arms talks - including China - Moscow wanted five-way arms talks.

Russia has said it wants Britain and France - also nuclear powers - to be included in any talks.

"The U.S. is proposing a three-way talks format and we want a five-way format. We are going round in circles," said Ryabkov.

Ryabkov also linked progress on agreeing a new nuclear treaty to Washington's wider policy towards Russia at a time when Trump says he is exploring how to end the war in Ukraine as the Russian economy tries to weather the toughest Western sanctions ever.

"As for (renewing) New START, as Putin has said, nothing prevents us from holding talks and we are ready for that. But this depends on whether we'll see a real shift in Washington's policy towards Russia," said Ryabkov.

"But this hasn't happened yet and it's therefore premature to talk about this. The clock is running down."

(Reporting by Dmitry Antonov in Moscow. Writing by Andrew Osborn in London; Editing by Guy Faulconbridge)