Nato has accused Russia of stoking tensions in Europe with the deployment of anti-ship missiles to its westernmost Baltic region.
The alliance said Moscow's decision to send Bastion missile launchers to Kaliningrad, which borders Nato members Poland and Lithuania, was "aggressive military posturing".
The move would do nothing to "lower tensions or restore predictability to our relations", it told the Associated Press.
The statement came shortly after US State Department spokesman John Kirby called Russia's plans to permanently deploy its S-400 air missile defence system and ballistic Iskander missiles to Kaliningrad "destabilising to European security".
Dmitry Peskov, a Kremlin spokesman, hit back at Kirby's comments yesterday, calling Nato an "aggressive" military alliance.