The foreign secretary has written to Washington over claims that the CIA has used EU airports to move suspects to other countries for torture.
Campaigners claim flights stopped in eastern Europe en-route to Cuba
Jack Straw said the letter "expressed concern" on behalf of all EU countries and he was waiting for a response.
He spoke after human rights group Liberty urged police to probe allegations that the flights called at British airports.
The US government has said its laws have not been broken.
But it has refused to confirm or deny the existence of "secret prisons" in third countries.
Liberty has called for action within 14 days - or, it has said, it will go to court claiming police aided and abetted kidnap and torture.
The Foreign Office has said it had no evidence of such use of UK territory.
At a news conference with Italian Foreign Minister Gianfranco Fini, who is visiting the UK, Mr Straw said his letter "had gone".
He said he was waiting for a response from the US Secretary of State Condoleezza Rice and he would circulate the reply to all his foreign minister colleagues.
"Meanwhile, let me say, I think there is no purpose in speculating on allegations that are made on this side or the other side of the Atlantic," he said.
"These are allegations about a foreign government. We have taken the appropriate steps, which is to ask for clarification by that government."
The Guardian in September reported claims that at least 210 CIA flights had landed in the UK since the 11 September 2001 attacks on the US.
It is alleged at least 12 airports in England and Scotland have been used, with the busiest being Prestwick in Ayrshire where CIA aircraft landed more than 75 times.
Shami Chakrabarti, Liberty's director, told BBC Radio 4's Today programme: "The allegations, the suspicions, the circumstantial evidence if you like, gives serious enough concern that we should ask chief constables to do their duty.
"They have positive obligations under international law and under our human rights act to investigate, and that's what we ask them to do."
Liberal Democrat foreign affairs spokesman Menzies Campbell told Today: "We need full disclosure by the government.
"If in fact people are being moved from a jurisdiction where torture is illegal to a jurisdiction where torture is permissible, that seems to me to be wholly contrary to international law.
"If we are allowing facilities for aircraft carrying out those actions, then we are at the very least facilitating it; we may even be complicit in it."
Liberty has written to the chief constables of Bedfordshire, Cambridgeshire, Dorset, Essex, Hampshire, Kent, the Metropolitan Police, the Ministry of Defence police, Sussex, Thames Valley and West Midlands forces.
Because of the possibility of court action if police fail to respond, Scottish police operating under a different legal system have not been contacted, Liberty says.
The airports allegedly involved include Biggin Hill in Kent, Birmingham, Bournemouth, RAF Brize Norton in Oxfordshire, Farnborough, Gatwick, Heathrow, Luton, Mildenhall in Suffolk, RAF Northolt in north London, Stansted and Prestwick.