The United States and Russia said Friday they were on the verge of clinching a sweeping new nuclear disarmament pact, but signaled the bid to smooth final technical issues would slip into January.

US President Barack Obama and Russian President Dmitry Medvedev held their latest summit on the sidelines of the UN climate talks in Denmark, but dashed speculation that the long-awaited deal would be signed by the end of the year.

Obama said the two sides were "quite close" to clinching a framework to decommission hundreds of nuclear arms, and replace the 1991 Strategic Arms Reduction Treaty (START) which expired on December 5.

"I'm confident that it will be completed in a timely fashion. And I just want to thank President Medvedev for being a very effective partner in these negotiations," he said.

Medvedev made clear that only "a few technical details" now blocked the agreement, which will see further deep mutual cuts in the nuclear arsenals of the former Cold War foes.

"Our positions are very close and almost all the questions that we discussed over the last months have been closed," Medvedev said.

"A few technical details have remained which nevertheless need to be finalized in such an important agreement and I hope that we will do this in quite a short time."

"I hope that the result that we reach (in the new treaty) will reflect the character of good relations which we have with the US administration."

Both sides made clear after the START treaty lapsed that they hoped to conclude the new pact by the end of the year, officials said the holiday season would now intervene.

Medvedev's foreign policy advisor Sergei Prikhodko said the two sides would now "take a break" after weeks of intense talks in Geneva, until early next year. A senior US official privately gave a similar message.

The two sides purposely declined to name a date for a conclusion to the talks and the signing ceremony "so as not to put unnecessary pressure on the delegations," Prikhodko said.

Medvedev and Obama set a goal in July of slashing the number of warheads on either side to between 1,500 and 1,675 and the number of "carriers" capable of delivering them to between 500 and 1,100.

The United States has said it currently has some 2,200 nuclear warheads, while Russia is believed to have about 3,000.

The new treaty is the centerpiece of Obama's attempt to "reset" previously strained ties between Moscow and Washington, and would yield important symbolic weight in his top priority effort to quell nuclear proliferation.

The US president will also bill the new treaty as a rare clear foreign policy success in a crisis-haunted first year in office, and for Medvedev it will be represent a dividend for embracing Obama's "reset" policy.

The cordial mood at the US-Russia summit contrasted with the bruising, gruelling talks taking place in the bid to close on a new global warming pact in Copenhagen and the US-Russia diplomatic dance which preceded the talks.

On Thursday, Russian Foreign Minister Sergei Lavrov said the United States was slowing down the talks, amid last minute haggling over conditions for the new treaty.

The US side had given every indication in the run-up to Copenhagen that it was in no immediate rush to sign a deal -- possibly to showcase a foreign policy win for Obama early in the new year, not overshadowed by climate talks.

In a sign of the new warmth between the two sides, the leaders offered one another compliments of the season before parting in snow cloaked Copenhagen.

"We wish him a Merry Christmas and a Happy New Year," Obama said of Medvedev, who returned the compliment.

"I would like to say Merry Christmas and Happy New Year to you."