Kabul, Afghanistan ? The U.S. military on Saturday announced its second investigation in a week into allegations of prisoner abuse in Afghanistan, amid growing demands from rights groups for secretive U.S.-run jails across the country to be opened for outside scrutiny.

Army spokesman Lt. Col. Tucker Mansager gave few details of the latest allegations, which follow complaints earlier this week from an Afghan police officer who said he was beaten and sexually assaulted during 40 days in custody last summer.

“On Thursday, coalition leaders were notified of another allegation of detainee abuse. Upon notification, coalition forces launched an immediate investigation,” Mansager said at a news conference in the capital, Kabul.

He said the detainee was arrested last year and had since been released. He did not divulge who provided the information that prompted the new probe.

Human Rights groups have long complained of consistent allegations of abuse in American holding facilities across Afghanistan, where hundreds of suspected Taliban and al-Qaida fighters have been held without legal access or charge. The U.S. military classifies some of them “unlawful combatants.” Many have been transferred to Guantanamo Bay, Cuba.

The scandal over abuses at Abu Ghraib prison in Iraq appears to have spurred the military into a quick response to the recent reports of mistreatment in Afghanistan.

On Monday, the U.S. military opened a criminal investigation into complaints of mistreatment by an Afghan police officer, Sayed Nabi Siddiqui, after his graphic account of his detention was published in the media.

Siddiqui told The Associated Press that he was punched, stripped naked and had objects inserted in his anus in three U.S. holding facilities — before being released without charge.

U.S. soldiers stand guard by an Afghan prisoner near Zunchorah Village in this photo taken April 3. The U.S. military has launched its second probe into prisoner abuse in Afghanistan in a week, a spokesman said Saturday.