CIA Director John Brennan speaks during the agency’s third conference on national security at Goerge Washington University on Sept. 20. (Mark Wilson/Getty Images)

Two men who were held at a CIA prison in Afghanistan have told a human rights group that they were subjected to a version of waterboarding at a detention site where the agency has insisted the brutal method was never used.

The allegations were detailed in a report released Monday by Human Rights Watch based on extensive interviews with two Tunisian men who were returned to that country last year after spending 13 years in U.S. custody, almost all of it at a prison complex at Bagram air base in Afghanistan.

Ridha al-Najjar and Lotfi al-Arabi El Gherissi both recounted being strapped to a board, spun around and doused with water until left gasping for air, according to the report.

The torture they described closely resembles the most notorious of the interrogation methods the CIA used on terrorism suspects after the Sept. 11, 2001, attacks, adding to the suspicion that the technique was employed more broadly than the agency has publicly acknowledged.

An exhaustive Senate investigation of the interrogation program noted that CIA officials could never explain a photograph found in the agency’s records of a waterboard-like apparatus at the so-called “Salt Pit” prison complex in Afghanistan, where both Najjar and Gherissi were held.

The CIA has for years maintained that only three prisoners, including self-proclaimed  9/11 mastermind Khalid Sheik Mohammed, were subjected to waterboarding, and that the method was only used at sites outside Afghanistan.

“CIA reviewed its records and found nothing to support these new claims,” an agency spokesman said.

In separate interviews, Najjar and Gherissi said they endured other types of brutal treatment not previously identified in any of the numerous investigations of the CIA interrogation program, which was dismantled shortly after President Obama took office in 2009.

Both said they were taken into a room equipped with what appeared to be an electric chair. “It had clips with wires attached to it intended to fit on fingers, and a helmet with wires,” the report said. Gherissi told Human Rights Watch that “his interrogators put him in the chair and threatened to use it on him unless he gave them more information, though they did not.”

Laura Pitter, who conducted the interviews as senior U.S. national security counsel at Human Rights Watch, said that the men endured physical and emotional trauma for years without ever being charged or tried.

“These terrifying accounts of previously unreported CIA torture methods show how little the public still knows about the U.S. torture program,” Pitter said in a statement. “The release of these two men without the U.S. providing any assistance or redress for their torture and suffering also shows how much the U.S. still needs to do to put the CIA torture program behind it.”

Najjar, 51, was captured in a U.S. and Pakistani operation in May 2002 in the southern port city of Karachi. Gherissi was taken into custody four months later in Peshawar, near the Pakistani border with Afghanistan.

Their accounts depict a gruesome atmosphere at the Salt Pit site months before the November 2002 death at that compound of Gul Rahman, a detainee who was doused with water and left overnight in freezing temperatures.

A footnote to the Senate report described a harrowing interrogation plan for Najjar that called for the use of sleep deprivation and other techniques. The plan was distributed to top CIA officials at agency headquarters, including current director John Brennan, who at the time was deputy executive director.

Najjar was also identified in the agency’s internal files as an important source of information about Osama bin Laden’s courier, a critical break in the hunt for the al-Qaeda leader. But the Senate report indicates that Najjar provided this information in June 2002, shortly before being transferred to CIA custody.