Russia’s most senior military officer said Thursday that Moscow would strike and destroy NATO missile defense sites in Eastern Europe before they came online if the U.S. pushes ahead with deployment.

“A decision to use destructive force pre-emptively will be taken if the situation worsens,” Russian Chief of General Staff Nikolai Makarov said at an international missile defense conference in Moscow attended by senior U.S. and NATOofficials.

The threat comes as talks about the missile defense system, which the U.S. and its allies insist is aimed at Iranian missiles, appear to have stalled.