President Vladimir Putin has signed a law which suspends Russia's participation in a treaty limiting military forces in Europe.
The law will come into effect on 12 December
It follows its adoption earlier this month by the Russian parliament.
The Conventional Forces in Europe (CFE) Treaty, signed in 1990, limits the deployment of tanks, aircraft and other heavy conventional weapons.
Russia says the suspension is a reply to the non-ratification of the treaty by Nato countries.
The law will come into effect on 12 December, allowing Russia to boost its troop levels on its western and southern borders, although no imminent plans to this effect have been announced.
Nato members, led by the United States, have refused to ratify the CFE treaty until Moscow withdraws its troops from the former Soviet republics of Moldova and Georgia, as Russia had promised in 1999.