The White House said on Wednesday that the United States and Russia are "very close" to reaching a new nuclear disarmament treaty to replace the expired Strategic Arms Reduction Treaty (START).

"We are very close to having an agreement on a START treaty, but we won't have one until President Obama and his counterpart Medvedev have a chance to speak," White House spokesman Robert Gibbs told reporters at the daily press briefing.

Gibbs said the two presidents would speak in the coming days on "some things that need to be worked out," adding that the new treaty would be signed in Prague, capital of the Czech Republic, where President Obama announced his vision of a nuclear-free world on April 5, 2009.

Earlier reports quoted a Russian official as saying that the two countries had finalized "all documents for the signing of (a new) START," and that the new treaty would be signed in April in Prague.

Under the new and more ambitious initiative, the nuclear warheads held by the two super nuclear powers are expected to be reduced to 1,500 to 1,675, while the launchers limited to 500 to 1, 000.

The two leaders have vowed to work together in the spirit of the START treaty following its expiration on Dec. 5, 2009, in order to ensure that a new treaty on strategic arms can enter into force at the earliest possible date.

Both Obama and Medvedev see the arms control process as a vital step to boost mutual trust between the two countries, and to ensure other countries to work with them together for the nuclear- free world. The Obama administration will host a Nuclear Security Summit on April 12-13 in Washington.