President Barack Obama and Russian President Dmitry Medvedev, agreed on Friday to 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,” Mr. Obama declared.

Mr. Obama said the pact, to be signed 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 toward improved U.S.—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,” Mr. Obama said at the White House.

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