At least four detainees were freed from prisons controlled by the United Arab Emirates in southern Yemen where they had been held without charges for nearly a year. The release on Monday came days after The Associated Press revealed that hundreds of Yemeni prisoners swept up in anti-terror raids by Emirati-backed forces have been subjected to torture and sexual abuse.

In Aden's Beir Ahmed prison, hundreds of inmates were forced to undress and Emirati officers searched their anal cavities March 10, claiming to be looking for contraband cellphones.

A state prosecutor, Mohammed Ali Saleh, declined to say how many detainees were freed on Monday. Security officials told the AP that more prisoners are expected to be released in the coming days from different secret prisons in Aden. The officials spoke on condition of anonymity because they weren't authorized to speak to the media.

Yemeni Interior Minister Ahmed al-Maysari has said on previous occasions that he has no control over the prisons and he can't enter Aden without the Emiratis' permission. The UAE is a key U.S. ally whose secret prisons, where torture is said to be widespread, were first reported in an AP investigation last June. The AP has since identified at least five prisons where security forces use sexual torture to brutalize and break inmates.

The AP first asked the Pentagon about abuses committed by the UAE one year ago. Despite reports of torture documented by the AP from former and current detainees, human rights groups and the United Nations, Marine Maj. Adrian Rankine-Galloway, a Pentagon spokesman, said the U.S. has seen no evidence of detainee abuse in Yemen.

"U.S. forces are required to report credible allegations of detainee abuse," he said. "We have received no credible allegations that would substantiate the allegations put forth in your line of question/story."

U.S. officials have acknowledged that American forces receive intelligence from UAE partners and have participated in interrogations in Yemen. Rankine-Galloway said he could not comment on intelligence sharing with partners.