Prisoners lie in a newly renovated cell in Aden Central Prison, known as Mansoura, in this May 9, 2017 photo in Aden, Yemen. Another, closed section of the prison is part of a network of secret detention facilities run by the United Arab Emirates and its Yemeni allies, into which hundreds arrested on suspicion of al-Qaida links have disappeared. Some have been flown to an Emirati base in the nearby Horn of Africa, and some have been interrogated by American officials, witnesses said. (AP Photo/Maad El Zikry)
Prisoners lie in a newly renovated cell in Aden Central Prison, known as Mansoura, in this May 9, 2017 photo in Aden, Yemen. Another, closed section of the prison is part of a network of secret detention facilities run by the United Arab Emirates and its Yemeni allies, into which hundreds arrested on suspicion of al-Qaida links have disappeared. Some have been flown to an Emirati base in the nearby Horn of Africa, and some have been interrogated by American officials, witnesses said. (AP Photo/Maad El Zikry) Credit: Maad El Zikry

Mukalla, Yemen — Hundreds of men swept up in the hunt for al-Qaida militants have disappeared into a secret network of prisons in southern Yemen where abuse is routine and torture extreme — including the “grill,” in which the victim is tied to a spit like a roast and spun in a circle of fire, an Associated Press investigation has found.

Senior American defense officials acknowledged on Wednesday that U.S. forces have been involved in interrogations of detainees in Yemen but denied any participation in or knowledge of human rights abuses. Interrogating detainees who have been abused could violate international law, which prohibits complicity in torture.

The AP documented at least 18 clandestine lockups across southern Yemen run by the United Arab Emirates or by Yemeni forces created and trained by the Gulf nation, drawing on accounts from former detainees, families of prisoners, civil rights lawyers and Yemeni military officials. All are either hidden or off limits to Yemen’s government, which has been getting Emirati help in its civil war with rebels over the last two years.

The secret prisons are inside military bases, ports, an airport, private villas and even a nightclub. Some detainees have been flown to an Emirati base across the Red Sea in Eritrea, according to Yemen Interior Minister Hussein Arab and others.

Several U.S. defense officials, speaking on condition of anonymity to discuss the topic, told AP that American forces do participate in interrogations of detainees at locations in Yemen, provide questions for others to ask, and receive transcripts of interrogations from Emirati allies. They said U.S. senior military leaders were aware of allegations of torture at the prisons in Yemen, looked into them, but were satisfied that there had not been any abuse when U.S. forces were present.

“We always adhere to the highest standards of personal and professional conduct,” chief Defense Department spokeswoman Dana White said when presented with AP’s findings. “We would not turn a blind eye, because we are obligated to report any violations of human rights.”

In a statement to the AP, the UAE government denied the allegations.

“There are no secret detention centers and no torture of prisoners is done during interrogations.”

Inside war-torn Yemen, however, lawyers and families say nearly 2,000 men have disappeared into the clandestine prisons, a number so high that it has triggered near-weekly protests among families seeking information about missing sons, brothers and fathers.

None of the dozens of people interviewed by AP contended that American interrogators were involved in the actual abuses. Nevertheless, obtaining intelligence that may have been extracted by torture inflicted by another party would violate the International Convention Against Torture and could qualify as war crimes, said Ryan Goodman, a law professor at New York University who served as special counsel to the Defense Department until last year

At one main detention complex at Riyan airport in the southern city of Mukalla, former inmates described being crammed into shipping containers smeared with feces and blindfolded for weeks on end. They said they were beaten, trussed up on the “grill,” and sexually assaulted. According to a member of the Hadramawt Elite, a Yemeni security force set up by the UAE, American forces were at times only yards away. He requested anonymity because he was not authorized to discuss the matter.

“We could hear the screams,” said a former detainee held for six months at Riyan airport. “The entire place is gripped by fear. Almost everyone is sick, the rest are near death. Anyone who complains heads directly to the torture chamber.” He was flogged with wires, part of the frequent beatings inflicted by guards against all the detainees. He also said he was inside a metal shipping container when the guards lit a fire underneath to fill it with smoke.

Like other ex-detainees, he spoke on condition of anonymity for fear of being arrested again. The AP interviewed him in person in Yemen after his release from detention.

The AP interviewed 10 former prisoners, as well as a dozen officials in the Yemeni government, military and security services and nearly 20 relatives of detainees. The chief of Riyan prison did not reply to requests for comment.

Laura Pitter, senior national security counsel at Human Rights Watch, said the abuses “show that the U.S. hasn’t learned the lesson that cooperating with forces that are torturing detainees and ripping families apart is not an effective way to fight extremist groups.” Human Rights Watch issued a report on Thursday documenting torture and forced disappearances at the UAE-run prisons and calling on the Emirates to protect detainees’ rights.

Amnesty International called for a U.N.-led investigation “into the UAE’s and other parties’ role in setting up this horrific network of torture” and into allegations the U.S. interrogated detainees or received information possibly obtained from torture. “It would be a stretch to believe the U.S. did not know or could not have known that there was a real risk of torture,” said Amnesty’s director of research in the Middle East, Lynn Maalouf.

Defense Secretary James Mattis has praised the UAE as “Little Sparta” for its outsized role in fighting against al-Qaida.