The pact is the linchpin of the nuclear arms control regime between the former Cold War foes and the main product of the 2010 "reset", a period of warmer ties that have since chilled.

The source said the ministry was studying the possibility of suspending on-site inspections agreed in the Strategic Arms Reduction Treaty (START) between Moscow and Washington.

The United States suspended military cooperation such as joint exercises and port visits with Russia on Monday as Washington sought ways to punish Moscow for its intervention in Ukraine.

"The ungrounded threats to Russia from the U.S. and NATO over its Ukrainian policy are regarded by us as an unfriendly gesture and allow us to announce force majeure," the unnamed source was quoted as saying by the state-owned RIA Novosti news agency.

"We are ready to take this step as a response to the Pentagon's statements about suspension of engagements between the armies of Russia and the U.S.," the source added.

"There could be no normal and regular bilateral contacts about adhering to the agreements against the background of ... the U.S. 'sanctions'," the source added.

In the latest version of the START treaty, originally agreed in 1991, the United States and Russia pledged to cap the numbers of their deployed strategic nuclear warheads to 1,550 each and limit the numbers of strategic nuclear missile launchers to 800 by 2018.

The treaty allows each side to conduct 18 on-site inspections per year in the other country.