The United States has voiced concern after reports Russia had moved short-range missiles to its westernmost region bordering Poland and Lithuania.
The State Department said Washington had urged Moscow not to destabilize the region.
Spokeswoman Marie Harf said Washington had passed on to Moscow regional concerns about the reported deployment of the Iskander missiles in the Kaliningrad area.
The advanced version of the Iskander has a range of 500 kilometers. It can also carry nuclear warheads.
Poland and three Baltic states on December 16 expressed alarm that the missiles would be close to their borders.
Moscow has long threatened to deploy the missiles in Kaliningrad in response to a planned U.S. missile-defense system.
Defense Secretary Chuck Hagel told his Russian counterpart Sergei Shoigu on December 16 that a preliminary nuclear deal with Iran "does not eliminate the need" for the shield.
Based on reporting by AFP and AP