President Dmitry Medvedev said today Russia would respond militarily to the deployment of US missiles close to its borders under an American missile shield plan.
US Secretary of State Condoleezza Rice signed an agreement in Poland last week on deployment of 10 US interceptor rockets there. Washington says the shield, also involving tracking systems in the Czech Republic, is intended to protect against launches by rogue states - a reference principally to Iran.
"These missiles are close to our borders and constitute a threat to us," Mr Medvedev told Al-Jazeera television. "This will create additional tension and we will have to respond to it in some way, naturally using military means."
Russia rejects US arguments for the shield and presents it as a move threatening its nuclear defences.
Mr Medvedev had spoken before of a possible military response, but today's remarks were the first on these lines since Ms Rice finalised the deal.
Russian military and political leaders have never specified what military steps they might take.
Some military officials have suggested deployment of missiles in Kaliningrad region, Russia's Baltic enclave bordering Poland and Lithuania, and in ex-Soviet ally Belarus could be an option.