President Barack Obama said on Friday that the United States and Russia are "quite close" to agreeing on a new arms control treaty.
The new deal would replace the 1991 Strategic Arms Reduction Treaty, or START I, that expired Dec. 5.
Emerging from a private meeting with Russian President Dmitry Medvedev held on the sidelines of the climate summit in Copenhagen, Obama expressed confidence that a successor pact will be agreed to in a "timely fashion," adding that technical details required further work.
At a summit in Moscow in July, Obama and Medvedev agreed to cut the number of nuclear warheads held by each country to between 1,500 and 1,675 within seven years as part of a broad new arms control agreement.
U.S. officials had earlier downplayed prospects for rapid progress in arms reduction talks after a Russian Foreign Ministry spokesman Andrei Nesterenko said negotiators could reach a new deal on Friday.
Nesterenko had voiced hope that U.S. and Russian negotiators at negotiations in Geneva could quickly iron out the remaining disagreements, possibly within hours.
"We hope that all remaining issues will be settled in the nearest time, maybe even within the next few hours," he said.
Later a Russian lawmaker who closely follows the negotiations, Konstantin Kosachev, said "an agreement was successfully concluded literally today."
"All that is left is the technical details, which remain to be finalized down to the last comma," the Interfax agency quoted him as saying.
Officials in Washington had said the talks were bogged down and appeared unlikely to be concluded by the year's end as the White House had hoped. The new deal should replace the 1991 Strategic Arms Reduction Treaty, or START I, that expired Dec. 5.