Human rights groups, lawyers and several Western diplomats assert hundreds of prisoners, who include women and children, have been transferred secretly and illegally in recent months from Kenya and Somalia to Ethiopia, where they are kept without charge or access to lawyers and families.
The detainees include at least one U.S. citizen and some are from Canada, Sweden and France, according to a list compiled by a Kenyan Muslim rights group and flight manifests obtained by AP.
Some were swept up by Ethiopian troops that drove a radical Islamist government out of neighboring Somalia late last year. Others have been deported from Kenya, where many Somalis have fled the continuing violence in their homeland.
Ethiopia, which denies holding secret prisoners, is a country with a long history of human rights abuses. In recent years, it has also been a key U.S. ally in the fight against al Qaeda, which has been trying to sink roots among Muslims in the Horn of Africa.
U.S. government officials contacted by AP acknowledged questioning prisoners in Ethiopia. But they said American agents were following the law and were fully justified in their actions because they are investigating past attacks and current threats of terrorism.
The prisoners were never in American custody, said an FBI spokesman, Richard Kolko, who denied the agency would support or be party to illegal arrests. He said U.S. agents were allowed limited access by governments in the Horn of Africa to question prisoners as part of the FBI's counter-terrorism work.
Western security officials, who insisted on anonymity because the issue related to security matters, told AP that among those held were well-known suspects with strong links to al Qaeda.
But some U.S. allies have expressed consternation at the transfers to the prisons. One Western diplomat in Nairobi, who agreed to speak to AP only if not quoted to avoid angering U.S. officials, said he sees the United States as playing a guiding role in the operation.
John Sifton, a Human Rights Watch expert on counter-terrorism, went further. He said in an e-mail that the United States has acted as "ringleader" in what he labeled a "decentralized, outsourced Guantanamo."
Details of the arrests, transfers and interrogations slowly emerged as AP and human rights groups investigated the disappearances, diplomats tracked their missing citizens and the first detainees to be released told their stories.
One investigator from an international human rights group, who spoke on condition of anonymity because the person was not authorized to speak to the media, said Ethiopia had secret jails at three locations: Addis Ababa, the capital; an Ethiopian air base 37 miles east of the capital; and the far eastern desert close to the Somali border.
More than 100 of the detainees were originally arrested in Kenya in January, after almost all of them fled Somalia because of the intervention by Ethiopian troops accompanied by U.S. special forces advisers, according to Kenyan police reports and U.S. military officials.
Those people were then deported in clandestine pre-dawn flights to Somalia, according to the Kenya Muslim Human Rights Forum and airline documents. At least 19 were women and 15 were children.
In Somalia, they were handed over to Ethiopian intelligence officers and secretly flown to Ethiopia, where they are now in detention, the New York-based Human Rights Watch says.
A further 200 people, also captured in Somalia, were mainly Ethiopian rebels who backed the Somali Islamist movement, according to one rights group and a Somali government official, who spoke on condition of anonymity because he did not want to jeopardize his job. Those prisoners also were taken to Ethiopia, human rights groups say.
Kenya continues to arrest hundreds of people for illegally crossing over from Somalia. But it is not clear if deportations continue.
The Pentagon announced last week that one Kenyan al Qaeda suspect who fled Somalia, Mohamed Abul Malik, was arrested and flown to the U.S. detention center at Guantanamo Bay, Cuba.
When contacted by AP, Ethiopian officials denied that they held secret prisoners or that any detainees were questioned by U.S. officials.
"No such kind of secret prisons exist in Ethiopia," said Bereket Simon, special adviser to Prime Minister Meles Zenawi. He declined to comment further.