Russia may suspend nuclear arms inspections in a treaty with the US in reaction to Western sanctions over Ukraine, Russian news agencies quoted an unnamed defence ministry source as saying.
"The ungrounded threats to Russia from the US 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 US," the source added.
Barack Obama warned Russia that the West will be forced to apply a cost to Moscow if it fails to change course in its dispute with Ukraine.
The ballot paper that the people of Crimea will use in Sunday's referendum was published today
Vitali Klitschko's visit to the eastern city of Donetsk is clearly an attempt to try to ease the divisions with Ukraine.