By DESMOND BUTLER and MAGGIE MICHAEL, The Associated Press

A renovated building in Aden Central Prison, known as Mansoura, is shown in this May 9, 2017, photo in Aden, Yemen. (AP Photo/Maad El Zikry)

WASHINGTON (AP) — Pressure mounted on the U.S. Defense Department Friday after multiple U.S. senators called for investigations into reports that U.S. military interrogators worked with forces from the United Arab Emirates who are accused of torturing detainees in Yemen.

John McCain, Republican chairman of the Senate Armed Services Committee, and the ranking Democrat, Jack Reed, called the reports "deeply disturbing."

The reports were revealed in an investigation by The Associated Press published Thursday.

That same day, McCain and Reed wrote a letter to Defense Secretary Jim Mattis asking him to conduct an immediate review of the reported abuse and what U.S. forces knew.

"Even the suggestion that the United States tolerates torture by our foreign partners compromises our national security mission by undermining the moral principle that distinguishes us from our enemies— our belief that all people possess basic human rights," the senators wrote Mattis . "We are confident that you find these allegations as extremely troubling as we do."

Democratic Sen. Patrick Leahy, Vice Chairman of the Senate Appropriations Committee, also called for an investigation and noted that support for the UAE forces could violate a law he wrote that forbids funding to known human rights violators.

"Reports of acts of torture by agents of a government that is supported by the United States, and the possibility that U.S. military personnel may have been aware of it, should ring alarm bells at the Department of Defense," Leahy said in a statement to the AP.

The AP's report detailed a network of secret prisons across southern Yemen where hundreds are detained in the hunt for al-Qaida militants and held without charges. American defense officials confirmed to the AP that U.S. forces have interrogated some detainees in Yemen but denied any participation in, or knowledge of, human rights abuses.

Defense officials told the AP that the department had looked into reports of torture and concluded that its personnel were not involved or aware of any abuse. The American officials confirmed that the U.S. provides questions to the Emiratis and receives transcripts of their interrogations. The officials said the U.S. also provides information to the UAE on suspected al-Qaida militants that the U.S. believes should be picked up or questioned.

Yemeni Brig. Gen. Farag Salem al-Bahsani, commander of the Mukalla-based 2nd Military District, told the AP that many of those men were later arrested.

"I'm troubled by the Pentagon's legalistic responses to these reports that U.S. officials worked in facilities where torture was widespread," Democratic Sen. Ron Wyden said in a statement. "U.S. allies have an obligation not to torture and the bar for the U.S. is higher than 'torture is OK if we don't see it.'"

The American Civil Liberties Union also said Friday that it had filed a Freedom of Information Act request for U.S. records related to the interrogations.

The 18 lock-ups are run by the UAE and by Yemeni forces it created, according to accounts from former detainees, families of prisoners, civil rights lawyers and Yemeni military officials. At the Riyan airport in the southern Yemeni city of Mukalla, former inmates described shipping containers smeared with feces and crammed with blindfolded detainees. They said they were beaten, roasted alive on a spit and sexually assaulted, among other abuse. One witness, who is a member of a Yemeni security force, said American forces were at times only yards (meters) away.

The UAE Ministry of Foreign Affairs said in a statement Friday that the allegations are "completely untrue" and a "political game" by Yemeni militias to discredit a Saudi-led coalition that includes the UAE. It says it does not run or oversee any prisons in Yemen, and that any such facilities are under "the jurisdiction of the Yemeni legitimate authorities."

Most of the clandestine sites are run by either the Hadramawt Elite or Security Belt, Yemeni forces that were created, trained and financed by the UAE. Officially, they are under the authority of Yemen's internationally recognized government, but multiple Yemeni government officials told the AP they have no control over them and they answer to the Emiratis.

At least three of the prisons, however, are directly run by the Emirates, along with a fourth prison housing Yemenis at an Emirati base in Eritrea, according to four senior Yemeni government and military officials, former detainees and families of prisoners.

At Riyan Airport prison in the southern Yemeni city of Mukalla, six former detainees described hundreds of prisoners held in shipping containers and gave extensive accounts of abuses, saying the officers in charge and those conducting interrogations were Emiratis. Families held frequent protests outside Riyan seeking news about loved ones imprisoned there. Several relatives of prisoners told the AP that they spoke repeatedly with the Emirati officer in charge of the site, who identified himself only by a pseudonym, Abu Ahmed, trying to secure their relatives' release.

The former detainees and the relatives of prisoners spoke on condition of anonymity fearing retaliation against themselves or their loved ones.

"We request that you direct an immediate review of the facts and circumstances related to these alleged abuses, including U.S. support to the Emirati and Yemeni partner forces that were purportedly involved," the lawmakers wrote.

McCain, a Navy pilot during the Vietnam War, was captured after his plane was shot down in 1967. He was imprisoned for more than five and half years and tortured repeatedly before he was released in 1973. In the Senate, McCain has criticized harsh treatment of terror suspects by the CIA at "black site" prisons and was a key sponsor of the 2005 Detainee Treatment Act prohibiting inhumane treatment of prisoners.

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Michael reported from Cairo. Stephen Braun contributed to this report.

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Follow Maggie Michael on Twitter at https://twitter.com/mokhbersahafi and Desmond Butler at https://twitter.com/desmondbutler