Russian President Dmitry Medvedev gestures as at a meeting on economic issues at the Gorki presidential residence outside Moscow on Friday. (RIA Novosti, Dmitry Astakhov,Presidential Press Service/Associated Press)

Russian President Dmitry Medvedev on Friday signed the ratification of a nuclear arms cut pact with the United States, the centrepiece of President Barack Obama's efforts to reset ties with Moscow.

The treaty, known as New START, limits each country to 1,550 strategic warheads, down from the current ceiling of 2,200, and also re-establishes a system for monitoring that ended in December 2009 with the expiration of a previous arms deal.

In a statement to his security council on Friday, Medvedev said the pact will take effect when the ratification documents are exchanged by Russian Foreign Minister Sergey Lavrov and American Secretary of State Hillary Clinton.

The pact was approved by the U.S. Senate last month after Obama pressed strongly for its passage, telephoning a handful of hesitant Republicans to lock in their votes.

Aging Soviet-built-missiles still form the core of Russia's nuclear forces, and the military has struggled to build their replacement.

NATO has approved a plan for a U.S.-led missile defence in Europe last fall and invited Russia to join.

Medvedev was receptive of NATO's proposal, but has not made a definite commitment.