In another sign of deteriorating relations between the United States and Russia, the U.S. government said on Monday that Moscow had violated the Intermediate Range Nuclear Forces treaty, and urged immediate bilateral talks on the issue.

The Cold War treaty, ratified in 1988, was designed to eliminate ground-launched cruise missiles with ranges of 500 to 5,500 km (310 to 3,400 miles).

"This is a very serious matter which we have attempted to address with Russia for some time now," an administration official said in a statement.

"We encourage Russia to return to compliance with its obligations under the treaty and to eliminate any prohibited items in a verifiable manner," the official said.