CAIRO — Human Rights Watch said it has uncovered evidence of a wider use of waterboarding than previously acknowledged by the CIA, in a report Thursday detailing brutal treatment of detainees at US-run lockups abroad after the 9/11 attacks.

The accounts by two former Libyan detainees who said they underwent simulated drowning emerged only days after the Justice Department closed its investigation of the CIA’s use of severe interrogation methods. Investigators said they could not prove any agents crossed the lines authorized by President George W. Bush’s administration in the program of detention and rendition.

Any new instances of waterboarding, however, would go beyond the three that the CIA has said were authorized.

The 154-page report features interviews by the New York-based group with 14 Libyan dissident exiles. They describe systematic abuses while they were held in US-led detention centers in Afghanistan — some as long as two years — or in US-led interrogations in Pakistan, Morocco, Thailand, Sudan, and elsewhere before the Americans handed them over to Libya.

The report also paints a more complete picture of Washington’s close cooperation with the regime of Libya’s former dictator Moammar Khadafy. Islamist opponents of Khadafy detained by the United States were handed over to Libya with only thin ‘‘diplomatic assurances’’ they would be properly treated, and several of them were subsequently tortured, Human Rights Watch said.

‘The scope of the Bush administration abuse appears far broader than previously acknowledged.’

‘‘Not only did the US deliver [Khadafy] his enemies on a silver platter, but it seems the CIA tortured many of them first,” said Laura Pitter, counterterrorism adviser at Human Rights Watch and author of the report.

‘‘The scope of the Bush administration abuse appears far broader than previously acknowledged,’’ she said.

Asked about the new waterboarding claim, CIA spokeswoman Jennifer Youngblood said the agency ‘‘has been on the record that there are three substantiated cases’’ of its use.

She said she could not comment on the specific allegations but noted the Justice Department’s decision not to prosecute after it ‘‘exhaustively reviewed the treatment of more than 100 detainees in the post-9/11 period — including allegations involving unauthorized interrogation techniques.’’

Bush, Vice President Dick Cheney, and the CIA have said that waterboarding was used only on three senior Al Qaeda suspects at secret CIA black sites in Thailand and Poland — Khaled Sheikh Mohammed, Aby Zubayda, and Abd al-Rahman al-Nashiri, all currently being held at Guantanamo Bay, Cuba.

The technique involves pouring water on a hooded detainee’s nose and mouth until he feels he is drowning. Rights groups and some Obama administration officials say waterboarding and other severe techniques authorized by the CIA constitute torture, while Bush administration officials argue they do not. The Obama administration has ordered a halt to waterboarding and many of the harsh techniques.

The 14 Libyans interviewed by Human Rights Watch were swept up in the American hunt for Islamic militants and Al Qaeda figures around the world after the Sept. 11, 2001 attacks. They were mostly members of the anti-Khadafy Libyan Islamic Fighting Group who fled in the 1980s and 1990s to Pakistan, Afghanistan, and African countries. The group ran training camps in Afghanistan at the same time Al Qaeda was based there but it largely shunned Osama bin Laden and his campaign against the United States, focusing instead on fighting Khadafy.

Ironically, the United States turned around and helped the Libyan opposition overthrow Khadafy in 2011. Now several of the 14 former detainees hold positions in the new Libyan government.

The accounts of simulated drowning came from Mohammed al-Shoroeiya and Khaled al-Sharif, who also described a gamut of abuses they went through — all reflecting the methods known to have been authorized by the CIA. The two were seized in Pakistan in April 2003 and taken to US-run prisons in Afghanistan, where Shoroeiya was held for 16 months and Sharif for two years before they were handed over to Libya.

In Afghanistan, they were shackled in cells for months in variety of positions, often naked in almost total darkness with music blaring continuously, left to defecate and urinate on themselves. For example, Sharif spent three weeks seated on the ground with his ankles and wrists chained to a ring in the cell’s wall, forcing him to keep his arms and legs elevated. He said he was taken out of his shackles once a day for a half-hour to eat.

For the first three months, they were not allowed to bathe. ‘‘We looked like monsters,’’ Shoroeiya said.

Shoroeiya described being locked naked for a day and a half in a tall, tight, 1½-foot-wide chamber with his hands chained above his head, with no food as Western music blasted loudly from speakers next to his ears the entire time.