An investigation into claims that the CIA held al-Qa'ida suspects in secret prisons in Europe has been stepped up, with 45 countries being sent a formal demand to provide information.
Austria's air force is investigating reports that a US transport plane containing suspected terrorist captives passed through the neutral country's air space in 2003. And Denmark is to ask US authorities for details about claims that detainees were flown across its territory. Two eastern European countries are said to be involved, and the UK presidency of the EU is sending a letter to the US seeking more information.
Terry Davis, the secretary general of the Council of Europe, set a 21 February deadline for his 45 member nations to answer questions on overflights, landings and possible secret detention centres.
Dick Marty, a Swiss MP, said he was investigating the flight plans of 31 aircraft that landed in Europe in recent years, but he believes the suspected detention centres are likely to be small, and have probably been closed. He appealed to the UN, Nato, the EU and Eurocontrol, which coordinates European air traffic navigation, for help.
Human Rights Watch has identified the Kogalniceanu military airfield in Romania and Poland's Szczytno-Szymany airport as possible secret detention centres, basing its claim on flight logs of CIA aircraft.
Mr Marty believes the other airports that might have been used include Palma de Majorca, Larnaca in Cyprus, Shannon in Ireland, and the US air base at Ramstein in Germany.
Sweden says a plane with possible CIA links has landed in the country three times since 2002. Denmark has identified 14 suspect flights. Norway has identified three.