The US Defence Secretary Robert Gates has confirmed the US will go ahead with plans to install parts of a missile defence shield in eastern Europe.
Mr Gates said the US would proceed with missile defence in Europe
He said Washington viewed a Russian offer to use a base in Azerbaijan as an additional capability not a substitute.
The US says the shield is necessary to protect against any missile attacks from "rogue states".
Russia recently threatened to target missiles against Europe if the US went ahead with the shield.
"I was very explicit in the meeting that we saw the Azeri radar as an additional capability, and that we intended to proceed with the radar... in the Czech Republic," Mr Gates said at a Nato meeting of defence ministers in Brussels.
The meeting was also attended by the Russian Defence Minister Anatoly Serdyukov, who made no comment on Mr Gates' statement.
Mr Gates said he welcomed the Russian offer of the base in Azerbaijan and said the US was willing "to work and partner with Russia on missile defence".
As part of an expansion of its anti-missile shield, the US is planning to install a sophisticated radar tracking system in the Czech Republic and 10 anti-missile interceptors in Poland.
The BBC's defence correspondent Rob Watson says Nato ministers have now in effect endorsed those plans by agreeing to look at how to protect parts of Europe not covered by the US plan.
"The Nato road map on missile defence is now clear. It's practical and agreed by all," said Nato Secretary General Jaap de Hoop Scheffer.
Bulgaria in particular, a staunch US ally, had expressed concerns that it might be left out of the US plan.
Nato has now ordered plans to be drawn up for a possible short-range missile defence system for Europe's southern flank.
Russia has said the American plan is a threat to its own security and a challenge to its influence in the region.
Russian President Vladimir Putin said Russia might aim its own missiles at Europe, but then offered the use of a former Soviet base in Azerbaijan for the US system instead of Poland and the Czech Republic.