Moscow, which has spooked the West with a troop buildup near Ukraine, last week unveiled a wish list of security proposals it wants to negotiate, including a promise NATO would give up any military activity in Eastern Europe and Ukraine. read more

Washington has said some of Russia's proposals are obviously unacceptable, but that the United States will respond some time this week with more concrete proposals on the format of any talks. read more

Konstantin Gavrilov, a Russian diplomat in Vienna, said that relations between Moscow and the NATO military alliance had reached a "moment of truth".

"The conversation needs to be serious and everyone in NATO understands perfectly well despite their strength and power that concrete political action needs to be taken, otherwise the alternative is a military-technical and military response from Russia," he was quoted as saying by RIA news agency.

Deputy Foreign Minister Sergei Ryabkov said that Moscow had so far received no response from the United States.

"I think they'll try to turn this into a slow-moving process, but we need it to be urgent, because the situation is very difficult, it is acute, it tends to become more complicated," he was quoted by RIA as saying.

Reporting by Tom Balmforth and Maria Kiselyova; editing by Mark Trevelyan