The British government faced renewed questions Thursday over whether the CIA has used the island of Diego Garcia, a leased U.K. territory in the Indian Ocean, to detain high-value suspects.

Prompted by an Al Jazeera report that published information from a classified U.S. Senate report, London-based human rights group Reprieve called on U.K. Foreign Secretary William Hague to release more information on the issue.

On Wednesday, it was reported that a Senate Intelligence Committee paper confirms that U.S. intelligence agents detained suspects on Diego Garcia, an island about 1,100 miles off the southern tip of India. The article cited two unnamed U.S. officials with knowledge of the classified document, which is set for declassification after an Intelligence Committee vote last week.

British authorities were in "full cooperation" with U.S. intelligence to use the island as a "black site" prison, secretly operated by the CIA, sources told Al Jazeera.

Reprieve's strategic director, Cori Crider, in a letter sent Thursday, asked Hague to clarify a series of statements by the British government denying that Diego Garcia was used as part of the CIA's secret detention program.

In one such statement in late 2011, Minister for Europe David Lidington denied allegations that the CIA had used Diego Garcia to hold suspects.

"Aside from the two cases of rendition through Diego Garcia (British Indian Ocean Territories) in 2002, the U.S. government has confirmed that there have been no other instances in which U.S. intelligence flights landed in the U.K.," Lidington said in an emailed response to Reprieve in 2011.

The comment followed the legal rights charity's claim that its clients Abdul-Hakim Belhaj and Fatima Boudchar were tortured by British intelligence agency MI6 and the CIA and repatriated in March 2004 to Libya — then under the control of toppled strongman Muammar Gaddafi — via Diego Garcia.

Lidington said no flights with a detainee on board landed on the island in March 2004.

In the latest push for clarity from the U.K. government, Reprieve has again asked Hague whether U.S. detainees were in fact held at Diego Garcia and if the British government was aware of their detention.

A spokeswoman at the U.K. Foreign Office declined to comment on Al Jazeera's report on CIA black sites.

Al Jazeera also reported on Wednesday that, according to sources, more than 100 CIA detainees were held in similar secret prisons in Afghanistan and Morocco, where they were subjected to torture.

Al Jazeera