U.S. officials said Thursday they want negotiations with Russia to produce a replacement deal for the Strategic Arms Reduction Treaty (START) by the end of the year.

State Department spokesman Philip Crowley said during a daily briefing that the United States want to "see this get done as quickly as possible. The presidents have set a goal of having this accomplished by the end of the year."

He said he hoped Assistant Secretary of State Rose Gottemoeller, who leads the U.S. negotiation team, "wouldn't have to give up other holidays to get there." Gottemoeller stayed in Geneva for the negotiations during Thanksgiving holidays last month.

Earlier this week, Russian media cited Kremlin officials as saying they wanted a deal by December 18.

Hillary Rodham Clinton, secretary of state, said earlier in the day a new deal to reduce the two countries nuclear arms is just a "question of when."

"I think that both sides are committed to completing the START treaty," she said in a joint news conference with visiting Croatian Foreign Minister Goran Jandrokovic.

Crowley noted there were still sticking points, saying the talks involve "very complex issues, when you get down to...numbers and verification procedures."

"There are a handful of issues that have details attached to them...We've had Russian proposals, U.S. counterproposals, Russian counter-counterproposals. And that is where we are," Crowley said.

Steven Pifer, an expert on arms control and proliferation in Brookings Institution, told Xinhua the main differences may be related to agreement on the number of launchers, and the verification procedures.

Under the START, which expired on Dec. 5, the United States and Russia should reduce their respective nuclear warheads to less than 6,000 and launchers to less than 1,600.

U.S. President Barack Obama and his Russian counterpart Dmitry Medvedev have agreed to reduce their nuclear arsenals by hammering out a new treaty, under which the nuclear warheads each side holds will be reduced to 1,500 to 1,675, while the launchers will be limited to 500 to 1,000.

Negotiators from the two countries, led by Gottemoeller and her Russian counterpart Anatoly Antonov, have been talking in Geneva, in order to resolve remaining differences.

In a joint statement issued on Friday, Obama and Medvedev said they will continue to work together in the spirit of the START treaty following its expiration, in order to ensure that a new treaty on strategic arms enter into force at the earliest possible date.