Bondage trilogy Fifty Shades of Grey is even more popular than the Koran at Cuba's Guantanamo Bay prison, it has been claimed.

According to US congressman Jim Moran, inmates at the controversial detention camp in Cuba, which holds 166 terrorism suspects apprehended since 9/11, prefer reading EL James' erotic novel than the Islamic holy book to occupy their time.

Earlier in July Moran toured Camp 7, the top-security facility that holds more than a dozen "high-value" prisoners, including five men charged with plotting the September 11 attacks on the United States in 2001.

Senator Tim Kaine, represenatives Frank Wolf and Gerry Connolly and William Lietzau, the Pentagon's chief of detainee policy, were also present for the site tour.

Moran said he was surprised to learn of Fifty Shades' popularity during his visit.

"Rather than the Koran, the book that is requested most by the (Camp 7 detainees) is Fifty Shades of Grey. They've read the entire series," Moran told the Huffington Post.

"I guess there's not much going on, these guys are going nowhere, so what the hell."

Guantanamo Bay has made headlines in recent months following appeals from Human Rights activists for its closure.

Obama has sought to close the detention camp since taking office in 2009, but measures to do so have become stuck in the US congress.

Lieutenant Colonel Samuel House, a spokesman for the prison camp, refused to comment on Moran's claims about the prisoners' choice of literature.

"We don't discuss our high-value detainees except in the most generic terms. Further, we do not discuss the assertions made by members of Congress," he was quoted by Reuters.

Books in the prison library range from Star Trek novelisations and stress reduction workbooks, to Agatha Christie mysteries. Religious tomes and Greek classic "The Odyssey are also available.