MOSCOW — A Russian military official says the country is preparing to deploy S-400 surface-to-air missiles in Kaliningrad, the western exclave that borders Poland and Lithuania, according to news reports. The ITAR-Tass and Interfax-AVN news agencies on Wednesday cited Col. Andrei Bobrun, a military spokesman, as saying the S-400s are undergoing tests in the southern Astrakhan region before deployment in Kaliningrad. He did not say when the deployment might start.

S-400s are mobile-launched air-defense missiles with a range of 120-400 kilometers (75-250 miles).

The announcement comes amid rising tension between the U.S. and Russia over Washington’s plans for a missile-shield system in Europe.

President Dmitry Medvedev last month threatened to deploy missiles to Kaliningrad and other areas to be aimed at U.S. missile defense sites.