Three Yemeni men allegedly abducted and mistreated by the US were probably held in eastern Europe, human rights group Amnesty International has said.
The US is accused of transporting suspects to secret jails abroad
The report, based on interviews with former detainees, also links the US practice of "rendition" to the torture or ill-treatment of terror suspects.
Washington has insisted it would never send detainees to places where they would be at risk of torture.
The CIA said it was aware of the report but declined to comment.
The 15,000-word report provides detailed accounts of the experiences of three Yemeni men who claim to have been held in at least four different secret US prisons between October 2003 and May 2005.
The men were allegedly held for 13 months at a so-called "black site", a secret facility believed to be run by the CIA, before they were returned to Yemen, Amnesty said.
In their statements, they gave detailed descriptions of travel times, changing climates and daylight hours which, although not conclusive, Amnesty says suggests they were held in Djibouti, Afghanistan and somewhere in eastern Europe.
The BBC's Rob Watson says although the report is highly critical of the US approach to terrorism suspects, it does not contain any suggestion from the three men that they were tortured by their American captors.
None of the three men were ever charged with any terrorism-related offence.
'Within the law'
The report also accused the US of using front companies to transfer individuals to countries where they have faced torture or ill-treatment.
Amnesty said it has records of nearly 1,000 flights, mostly using European airspace, which were made by planes that appear to have been permanently operated by the CIA through front companies.
It also said it had records of about 600 other flights made by planes confirmed as having been used at least temporarily by the CIA.
"The latest evidence shows how the US administration is manipulating commercial arrangements in order to be able to transfer people in violation of international law," said Amnesty International secretary general Irene Khan.
"It demonstrates the length to which the US government will go to conceal these abductions," she said in a statement.
The US government has said that the transfer of terror suspects is carried out according to US and international law.
However, Amnesty says the CIA is exploiting a loophole that allows private aircraft to land at foreign airports without having to inform local authorities - unlike government or military planes.
'Human rights violations'
Critics say it is difficult to prove the purpose of such flights and suggest the planes used by the CIA may have been simply carrying officials.
Amnesty said it has linked the aircraft to people who have been illegally transferred. It cites one plane known to have made over 100 stops at Guantanamo Bay.
The group warned that governments around the world may find themselves "complicit in serious human rights abuses" and urged them to take steps to prevent renditions.
Governments must insist that any aircraft used for an intelligence mission be declared a "state" flight and prohibit the use of airspace and airports for "renditions", it said.
It also urged governments to disclose the full extent of the practices and the fate of those whose whereabouts are still unknown.
Amnesty also called on the aviation sector to take steps to prevent "facilitating human rights violations", by ensuring they were aware of the end use of any aircraft they lease or operate.