Russia says it is prepared to use "destructive force pre-emptively" if the US goes ahead with controversial plans for a missile defence system based in Central Europe.
The warning came after the Russian defence minister said talks on missile defence were nearing a dead end.
Moscow fears that missile interceptors would be a threat to Russia's security.
But the US and NATO say they are intended to protect against attacks from Iran or North Korea.
Two days of talks opened yesterday in Moscow between Russia, the US and NATO.
Russia and the US have been at odds over the issue of missile defence since 2000, ever since the idea was first put forward by then-President George W Bush.