US officials on Wednesday declined to confirm a newspaper report that the United States and Russia had reached an "agreement in principle" to slash their nuclear weapons stockpiles.

The Wall Street Journal first reported on Tuesday that the first such pact in two decades was about to become a reality, but officials said they could not predict when negotiations would finally wrap up.

National Security Council spokesman Mike Hammer only referred to recent remarks by President Barack Obama and spoke of progress in talks when asked to comment on Tuesday's report.

"As the president said in his State of the Union address, the United States and Russia are completing negotiations' on an agreement," Hammer said.

"We continue to make progress, but will not make any predictions about when we will be finished with the remaining negotiations," Hammer said.

Nor could State Department officials immediately confirm a deal.

In Moscow, a Kremlin official said the deal could be signed this spring in Prague, the venue for Obama's keynote speech last year on nuclear disarmament.

"In expert circles close to the US side, Prague is being named as the venue for the signing," the unnamed official was quoted by Russian news agencies as saying.

"This choice is not being turned down in Moscow," the official added.

Separately, Russian President Dmitry Medvedev's chief foreign policy aide said the deal could be signed later this spring.

"March-April is a realistic timeframe" for signing a new nuclear disarmament treaty, Sergei Prikhodko said, according to Russian news agencies.

"On the whole, the text has been agreed upon though some minor discrepancies remain," he added.

The Journal said 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 Strategic Arms Reduction Treaty (START), which led to deep cuts in both nuclear arsenals after it was signed in 1991 before the collapse of the Soviet Union.

The Journal, citing administration and arms control officials, said US and Russian arms control negotiators reached an "agreement in principle" on the nuclear arms reduction pact.

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.