Germany says the US should include its Nato allies in discussions on the possible deployment of a missile defence shield in Europe.
The US says it does not need a Nato green light for the shield
The German Defence Minister, Franz Josef Jung, said "we should discuss developing such a defence measure within a Nato framework".
The US is negotiating with Poland and the Czech Republic over the deployment of a radar and 10 missile interceptors.
Russia has condemned the US plan and says it is developing new missiles.
Mr Jung said Russia's concerns should be addressed at an existing forum, the Nato-Russia Council. He was speaking on Friday after an EU defence ministers' meeting in Wiesbaden, Germany.
The head of the US Missile Defence Agency, Lt Gen Henry Obering, said in Brussels that a US "forward deployable radar" might also be set up in the Caucasus as part of the defence shield.
Lt Gen Obering: US is considering a radar in the Caucasus
Russia reacted coolly to his comments.
"Let them deploy it. It is their problem. We have everything we need to respond to all these deployments in a commensurate way," Russian air force commander Vladimir Mikhaylov told Rossiya TV.
Moscow has warned Poland and the Czech Republic that they risk being targeted by Russian missiles if they agree to host the US defence system.
The US says it wants the shield as protection against missiles that might be fired one day by a "rogue" state such as North Korea or Iran.
The Czech and Polish governments have given their approval in principle to the deployment on their territories of the defence system.
But the political situation, especially in the Czech Republic, is very delicate, as Prime Minister Mirek Topolanek has no majority in parliament and on Friday a poll showed that three-fifths of Czechs were opposed to having the US shield on their territory.