Russian President Dmitry Medvedev has signed the ratification of a nuclear arms cut pact with the United States, the centrepiece of US 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, Mr Medvedev said the pact will take effect when the ratification documents are exchanged by Russian foreign minister Sergey Lavrov and US secretary of state Hillary Clinton.
The pact was approved by the US Senate last month after Mr Obama pressed strongly for its passage, telephoning a handful of hesitant Republicans to lock in their votes.
Democrats sought to appease some Republican senators by allowing them to raise concerns about the treaty in an accompanying resolution.
The resolution did not affect the text of the treaty, but Russian legislators felt compelled to offer their own interpretation of the pact's provisions in their ratification bill and accompanying statements.
While the Senate resolution said the treaty should not restrict US plans to develop a missile defence system, the Russian ratification bill states that the treaty can only be fulfilled if emerging missile defence systems do not erode the Russian nuclear deterrent.
Defence Minister Anatoly Serdyukov said on Wednesday that Russia was working to develop its own missile defence system, but did not give any specifics.
Addressing concerns about Russia being forced to disarm under the treaty, he said that Russia now has a significantly smaller number of missiles and bombers than the treaty allows anyway. Ageing Soviet-built-missiles still form the core of Russia's nuclear forces, and the military has struggled to build their replacement.
Nato approved a plan for a US-led missile defence in Europe last year and invited Russia to join. Mr Medvedev was receptive of Nato's proposal but has not made a definite commitment.