Washington : US President Barack Obama and Russian President Dmitry Medvedev agreed yesterday to a sharp cuts in the nuclear arsenals of both nations in the most comprehensive arms control treaty in two decades. "We have turned words into action," Obama declared.

Obama said the pact, to be signed on April 8 in Prague, was part of his effort to reset relations with Russia and a step on a path toward "the peace and security of a world without nuclear weapons".

The agreement would require both sides to reduce their arsenals of long-range nuclear weapons by about a third, from 2,200 now to 1,500 each. The pact, replacing and expanding a 1991 treaty that expired in December, was a gesture towards improved US-Russian relations that have been badly frayed.

"In many ways, nuclear weapons represent both the darkest days of the Cold War, and the most troubling threats of our time. Today, we have taken another step forward in leaving behind the legacy of the 20th century while building a more secure future for our children," Obama said at the White House.

Both sides would have seven years after the treaty's ratification to carry out the approximately 30 per cent reduction in long-range nuclear weapons. The agreement also calls for smaller cuts to warheads and bombs based on planes, ships and land.

"We have turned words into action. We have made progress that is clear and concrete. And we have demonstrated the importance of American leadership — and American partnership — on behalf of our own security, and the world's," Obama said.

Though the agreement must still be ratified by the Senate and the Russian Duma before it takes effect, Obama and Medvedev plan to sign it next month in Prague — the city where last April, Obama delivered his signature speech on arms control committing America to the ultimate goal of "a world without nuclear weapons".

Speaking in the White House briefing room, Obama said that nuclear weapons "represent both the darkest days of the Cold War, and the most troubling threats of our time".

He said the treaty on the part of the two largest nuclear powers in the world would "send a clear signal that we intend to lead" the rest of the world in reducing the nuclear threat.

US Secretary of State Hillary Rodham Clinton noted that the US and Russia still possess more than 90 per cent of the world's nuclear weapons. "We do not need such large arsenals to protect our nation," she said.