Russia is suspending its last major nuclear disarmament treaty with the United States.
President Valdimir Putin announced the move during an address to the nation.
The New START Treaty commits Russia and the United States to limiting their stockpile of nuclear warheads.
It came into force in 2011 and was due to expire in 2026.
Putin also warned Washington that if the US resumes nuclear tests, Russia will do the same. His audience of lawmakers greeted the statement with applause.