"The treaty marks significant progress toward President Obama's vision of a world without nuclear weapons," U.S. Secretary of State Hillary Rodham Clinton said after exchanging ratification papers with Russian Foreign Minister Sergey Lavrov on the sidelines of an international security conference in Munich.

"Partnership with Russia is vital to our continued progress and to all that we hope to accomplish," she said. "We must build the habits of cooperation that let us rise above our differences to address urgent matters of global security together."

The New START treaty — the first major revamping of nuclear disarmament deals since the late Cold War era — was approved by the U.S. Senate in December after a bruising fight during which Obama pressed strongly for its passage. Russia ratified the deal last month.

Russia's Deputy Prime Minister Sergei Ivanov suggested that the two countries could build upon the new treaty in other areas, saying that "coordinated efforts" were needed in missile defense, and that Moscow also was willing to talk about tactical nuclear weapon reductions.

"We are ready to discuss this very complex topic in the framework of a comprehensive approach to strategic stability," he said.

He also stressed that any "hypothetical" negotiations on tactical nuclear weapons "must take into consideration not only Russia's or the U.S. nuclear arsenal but weapons systems of all nuclear and threshold" states.

The 10-year New START treaty, which can be extended by another five years, is a cornerstone of Obama's efforts to "reset" U.S. relations with Russia, and Clinton called it a "milestone in our strategic partnership."