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 states.

Russia recently threatened to target missiles against Europe if the US went ahead with the shield.

Speaking at a Nato meeting of defence ministers in Brussels, Mr Gates said: “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”.

The meeting was also attended by the Russian Defence Minister Anatoly Serdyukov, who made no comment on Mr Gates' statement.

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.

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.