Russia has warned Nato it could freeze its participation in a key arms control treaty in Europe, after talks on the issue ended in deadlock.
Russia says the CFE treaty has become "meaningless"
The talks in Vienna were aimed at reviewing the Conventional Forces in Europe (CFE) Treaty, which limits the number of non-nuclear weapons.
The Kremlin says the 1990 treaty is outdated and restricts its ability to move troops around its own territory.
Russia ratified the 1999 revised version, but Nato has not done so.
Nato states are first demanding the withdrawal of Russian forces from Georgia and Moldova, but Moscow says the issues are not linked.
"The current CFE treaty has for all intents and purposes become meaningless. It's no longer viable," Russian delegation chief Anatoly Antonov said after the four-day extraordinary talks called by Russia.
"But no-one listened to us. They continued to admonish us," Mr Antonov said.
He added that Russia's moratorium on honouring the treaty "will become a very real option" if dialogue on the issue continued to be stalled.
Russian President Vladimir Putin has warned that the CFE treaty - signed eight years after the Warsaw Pact was dissolved - no longer reflects the post-Cold War world.
On Friday, Nato issued a statement expressing regret that no deal had been reached.
But it urged Russia "to engage in continuing dialogue which would lead to a positive outcome in the future".
The BBC's diplomatic correspondent Jonathan Marcus says the CFE treaty harks back to another age and in many ways it is difficult to see quite why it is relevant today.
Russia was alarmed when the US withdrew from another Cold War agreement - the Anti-Ballistic Missile Treaty - in 2001.
Faced by a US administration that sees less and less value in such agreements, the Russians are signalling that what goes for Washington goes for them too, our correspondent says.