The United States said Thursday it is optimistic about completing negotiations "fairly quickly" with Russia for a new treaty to slash their nuclear weapons stockpiles.

However, State Department spokesman Philip Crowley declined to confirm remarks from an unnamed Kremlin official who said Wednesday a new Strategic Arms Reduction Treaty (START) could be signed this spring in Prague.

Crowley also declined to confirm a Wall Street Journal report Tuesday that the two sides have already reached an "agreement in principle" to replace the Cold War-era treaty that expired December 5.

"I think we are optimistic that with the START negotiations having reconvened this week in Geneva, that ... the remaining issues can be resolved and negotiations completed rather quickly," Crowley told reporters.

"With that said, I wouldn't put a particular time line on it," he said.

He had been asked to comment on an official quoted by Russian news agencies as saying the treaty would be signed in the spring in the Czech capital, where President Barack Obama gave a keynote speech last year on nuclear disarmament.

Crowley gave no direct answer when asked if an agreement in principle had been reached. "Negotiators are still at work," he replied.

The Wall Street Journal said Tuesday the two sides had agreed to lower the ceiling for deployed nuclear weapons from the 2,200 decided on in 1991 to between 1,500 and 1,675.

Any deal would mark a breakthrough in months of negotiations to replace the START, which led to deep cuts in both nuclear arsenals after it was signed in 1991 before the collapse of the Soviet Union.

It said the breakthrough in the negotiations came two weeks ago when National Security Adviser James Jones and Admiral Michael Mullen, the chairman of the joint chiefs of staff, went to Moscow to overcome stumbling blocks.

Those involved two issues on verification, sharing information on missile flight tests and inspections at missile production plants, it said.

The Wall Street Journal said the agreement was approved in principle last week during a telephone conversation between Obama and Russian President Dmitry Medvedev.