WASHINGTON, D.C., Apr 6 (OneWorld) - The Central Intelligence Agency (CIA) has used private aircraft and front companies to illegally transfer terror suspects to secret prisons in countries known to practice torture, Amnesty International has charged.

Specifically, the spy agency ''has used private aircraft operators and front companies to preserve the secrecy of 'rendition' flights,'' Amnesty said. It described rendition as ''a covert operation whereby people have been arrested or abducted, transferred and held in secret or handed over to countries where they have faced torture and other ill-treatment.''

The watchdog said it has records of nearly 1,000 suspicious flights apparently involving front companies and added that most of these flew over or made stops in Europe. Another 600 flights involved planes acknowledged to have been used by the CIA at least temporarily.

"One particular aircraft is known to have made over 100 stops in Guantanamo Bay," it said. "Another took [Egyptian cleric and terror suspect] Abu Omar to Egypt from Germany after he was kidnapped in Italy," Amnesty said. "Its owners have admitted leasing the plane to the CIA, but have said it is not used exclusively by the agency," Amnesty said.

The report, entitled ''Below the Radar: Secret Flights to Torture and Disappearance'' and released Wednesday, also provided detailed testimony and accounts in support of allegations that terror suspects had been held under inhumane conditions.

However, it offered no definite estimate of the number of secret flights used to illegally transfer terror suspects, as opposed to those that may have been sent on other missions.

Nor did it clearly identify Eastern European countries hosting or running secret detention centers also known as ''black sites.'' Rather, it parsed rendition survivors' testimony for clues and speculated about possible locations.

No Eastern European country has admitted involvement. Two U.S. allies named as prime suspects in the report--Bulgaria and Romania--have strongly denied it.

Even so, the report could add to pressure for greater disclosure in the United States and in the European Union (EU), where a parliamentary committee is probing possible collusion in the CIA scheme by bloc members and hopefuls.

The document also seems destined to stoke concern at home and misgivings abroad about U.S.-sanctioned torture, allegations of which have hounded Washington despite repeated assurances and some high-profile prosecutions of mostly low-level U.S. personnel involved in prisoner abuse at Iraq's Abu Ghraib prison.

Many in the human rights committee say the administration of President George W. Bush has failed to clamp down on torture and abuse by U.S. personnel and to exact accountability for past offenses. As a result, they add, U.S. personnel continue to engage in torture and abuse in Iraq and Afghanistan and at Guantanamo Bay.

Amnesty, Human Rights Watch, and other leading watchdogs long have maintained that extreme rendition violates international law. The practice predates the Bush administration but it is believed to have become common in the four-plus years since the Sep. 11, 2001 terrorist attacks on U.S. soil.

On Wednesday, Amnesty warned governments they may end up ''complicit in serious human rights abuses'' and urged them to take more effective action to prevent the use of their airspace and airports for renditions.

Amnesty further demanded that governments in transit and destination countries conduct and publish comprehensive inquiries into the magnitude of their involvement in rendition--and into ''the fate of those whose whereabouts are still unknown.''

Aviation companies, it added, must ''ensure that they are aware of the end use of any aircraft they lease or operate and that they do not facilitate human rights violations.''

U.S. officials have defended rendition as legal and as a necessary tool in the Bush administration's self-styled ''war on terror.''

Attorney General Alberto Gonzales has said anti-torture laws and treaties do not restrict interrogators overseas because the U.S. Constitution does not apply in prisons there.

Bush signed a bill late last year that outlaws the torture of detainees but he tacked on a stipulation reserving his right to sidestep the law.

International law bans torture and does not allow exceptions even in times of war or national emergency, rights groups have countered, adding that the ban extends to transferring people to places where they face a risk of torture.

The United States does not send terror suspects to any such place, federal officials have said, adding that Washington has insisted that governments receiving the prisoners furnish diplomatic assurances that they would not be tortured.

Amnesty dismissed the administration's argument, saying in its report that ''if the risk of torture or ill-treatment in custody is so great that the U.S.A. must seek assurances that the receiving state will not behave as it normally does, then the risk is obviously too great to permit the transfer.''

Amnesty and other rights groups have urged authorities to either charge and try terror suspects or release them on the basis of evidence.

The United States is not alone in deporting or seeking to boot terror suspects to alleged torture havens, Human Rights Watch reported last year. Others have included Austria, Britain, Canada, Germany, Georgia, the Netherlands, and Sweden. Receiving regimes have included Egypt, Syria, and Uzbekistan, where torture is a systemic human rights problem, the watchdog said.