BARACK Obama's ambitious goal of freeing the world of nuclear weapons won a significant boost on Wednesday night when Russia indicated that it had reached agreement with the US on a historic nuclear arms reduction treaty.

Kremlin officials said a document to replace the 1991 Start treaty had been agreed with Washington. A signing ceremony between Obama and Russia's president, Dmitry Medvedev, is likely to take place early next month in the Czech capital Prague, they said.

White House officials stopped short of announcing a done deal, but confirmed the US was “very close” to signing a new treaty with Russia. They suggested that the last remaining step was for the two presidents to agree to a signing date.

“We are, I think very close to having an agreement on a START treaty, but we won't have one until President Obama and his counterpart, Mr Medvedev, have a chance to speak,” said White House spokesman, Robert Gibbs. He suggested that would happen within a few days.

A spokesman for the Czech president, Vaclav Klaus, said a date for the signing had been agreed but would be announced later. The Americans are likely to prefer April 5, the first anniversary of Obama's speech in the Czech capital in which he outlined his vision of a nuclear-free world.

The treaty, which substantially reduces Russian and US nuclear arsenals and delivery systems, is a big achievement for Obama and his attempts to reset relations with Russia. Negotiators had been trying to reach agreement for nearly a year, and the previous treaty expired last December.

Wednesday's breakthrough followed US Secretary of State Hillary Clinton's visit to Moscow last week and last minute talks with Vladimir Putin, the prime minister. Putin had insisted there could only be a new treaty if the US linked nuclear reductions to its revised missile defence shield in Europe.

The White House's decision to site parts of its missile shield in Romania — and possibly Bulgaria — is known to have irked Putin. But he appears to have allowed Medvedev and Obama a mutual foreign policy success. Obama must now persuade sceptical Republicans to ratify the treaty.

One nuclear arms expert said the US and Russia may have amended the way nuclear missiles and launchers are counted to arrive at the figures agreed at a US-Russian presidential summit in Moscow last July.

Obama and Medvedev called for a reduction to between 1,500 and 1,675 warheads and 500 to 1,100 delivery systems including missiles and bombers. The expired treaty permits each side a maximum of 2,200 warheads and 1,600 launch vehicles.

No details had been published, but Yevgeny Myasnikov, a leading Moscow-based defence expert, said the new pact was likely to include a clause allowing the reductions to be reversible, so that both sides could reassemble nuclear warheads in an emergency. “There isn't much in the substance of this treaty,” he said.

The treaty would however allow Russia and the US to discuss more significant further strategic nuclear cuts, he said. “I think it's a good start. Both sides benefit from this. But further progress will take time and effort.”

A treaty will provide Obama with a much-needed foreign policy success. He had hoped to have the Start treaty signed and ratified by the Senate before a high-profile nuclear review summit in Washington next month. He had also hoped to have ratification of a comprehensive test ban treaty in place, but that is unlikely this year.

— The Guardian, London