Terror suspects held by the CIA were interrogated on the British owned island of Diego Garcia despite the repeated denials of London and Washington that any such incidents took place, a senior American official said today. Lawrence Wilkerson, who was the chief aide to former US Secretary of State Colin Powell, said the remote UK-administered military base in the Indian Ocean was used as a back-up location for nefarious activities", such as the questioning of prisoners in the wake of the 9/11 attacks. In an interview with the Vice News website, Mr Wilkerson said that Diego Garcia did not host a permanent CIA prison but was used as a back-up location to conduct interrogations. Mr Wilkerson, 70, who served as chief of staff to Mr Powell throughout the Iraq war, said he had not learnt of the CIA's alleged use of Diego Garcia until after he stepped down in 2005. He said that on the basis of his own experience while serving on the island in the 1980s and information from his sources, he believed it to be unlikely that any interrogations could have happened without the knowledge of British liaison staff who are in command of the base. The former Prime Minister Tony Blair and Foreign Secretary Jack Straw have previously denied any use of the coral atoll for rendition. It was reported last year by Al Jazeera that the Senate Intelligence Committee report, which provided an account of torture by the CIA, would confirm Diego Garcia was used for rendition "with the full co-operation of the UK". When the document was published the locations of black sites had been redacted.