U.S. Secretary of State Hillary Clinton urged her Russian colleague Sergei Lavrov to speed up work on the new arms reduction treaty, a State Department spokesman said.

The two diplomats have held a 15-minute phone conversation on Tuesday to discuss a new deal to replace the Strategic Arms Reduction Treaty (START 1), the cornerstone of post-Cold War arms control agreement which expired on December 5, 2009.

"She [Clinton] emphasized to the foreign minister that our negotiators are close to reaching an agreement and encouraged Russia to continue to move ahead, push hard so we can reach an agreement in the next couple of weeks," Philip Crowley told a media briefing late on Tuesday.

A senior Russian lawmaker Konstantin Kosachyov said on Wednesday the sides were likely to complete the talks in the next two or three weeks.

"We are at the point where we think that we can reach an agreement relatively quickly. And we are encouraging the Russian side to do its part," Crowley added. "There are still some details to be worked out and we hope we can do that in the coming days."