The US may delay activating its Europe-based missile defence shield, Defence Secretary Robert Gates says.

Mr Gates said the US had put new proposals to Russia, which has strongly opposed sites for the shield being set up in Poland and the Czech Republic.

The defence secretary said activation could be delayed until there was "definitive proof" of a missile threat from states such as Iran.

Mr Gates recently failed to win Russian support in talks in Moscow.

Russian presence

On Tuesday he met Czech Prime Minister Mirek Topolanek in Prague and said afterwards: "We would consider tying together activation of the sites in Poland and the Czech Republic with definitive proof of the threat - in other words, Iranian missile testing and so on."

Mr Gates also suggested Russian officials could also be present at the bases, although when asked about the possibility Mr Topolanek said: "No comment".

The missile shield system would see a radar site set up in the Czech Republic and a missile interceptor base in Poland.

Russia has vehemently opposed bases on the territories of former Warsaw Pact allies.

Mr Gates and US Secretary of State Condoleezza Rice received a frosty reception when they tried to sell the plan in Moscow.