MOSCOW — Russia has turned on a new incoming missile early warning system in its westernmost region in response to US plans for a missile shield in Europe.

President Dmitry Medvedev officially opened the new military early warning radar Tuesday, saying it shows Russia's readiness to respond to US missile defense plans.

Medvedev added, however, that the massive radar in the Kaliningrad region could be integrated in a joint NATO-Russia missile shield if a cooperation agreement is reached.

"I hope that our partners will perceive this move as the first signal of our country's readiness to respond in kind to the threats, which the missile defense system poses for our forces," Medvedev said.

Russia sees the US missile defense plans in Europe as a security challenge, even though Washington says they are aimed against a potential Iranian missile threat and can't pose a threat to Russia's nuclear deterrent.

In last week's televised address to the nation, Medvedev threatened to deploy missiles to Kaliningrad and other areas of Russia aimed at US missile defense sites, if the US and NATO fail to reach a deal assuaging Russian concerns.

A year ago, Moscow agreed to consider NATO's proposal to cooperate on the missile shield, but the talks have run into a deadlock over how the system should be operated. Russia has insisted that it should be run jointly, which NATO has rejected.

With no progress on a shared missile shield, Medvedev insisted that Russia wants firm and specific guarantees from Washington that its future missile defense potential will not be directed against Russia.

"We can't be satisfied with oral assurances that the system isn't aimed against Russia," Medvedev said Tuesday. "Regrettably, such oral statements don't guarantees the protection of our interests."

Washington's missile defense plans have been a key irritant in US-Russian relations since President Ronald Reagan's "Star Wars" plans that scared Moscow in the 1980s.