Interrogations of US prisoners took place at a CIA black site on the British overseas territory of Diego Garcia, a senior Bush administration official has told VICE News.

The island was used as a "transit location" for the US government's "nefarious activities" post-9/11 when other places were too full, dangerous, insecure, or unavailable, according to Lawrence Wilkerson, Colin Powell's former chief of staff.

There was no permanent detention facility such as the CIA facility in Poland, he told VICE News in a wide-ranging interview. His intelligence sources indicated to him that the island was however home to "a transit site where people were temporarily housed, let us say, and interrogated from time to time."

Wilkerson was Powell's chief of staff at the State Department from 2002 to 2005, but he did not learn of the CIA's activities on Diego Garcia until after leaving office. His information comes from four well-placed CIA and intelligence sources, including a veteran who participated in the renditions program, and a member of the Intelligence and Research Bureau at the State Department who was "very much plugged in to what was going on at the CIA."

Diego Garcia, a tiny atoll in the Indian Ocean, is a British territory that has been leased to the US, which regards it as an important strategic military outpost, since 1966. The British government has insisted that only two rendition flights have passed through Diego Garcia, both stopping there to refuel in 2002, but questions remain over the island's role in the CIA's post-9/11 interrogation program.

"No one has indicated there was a detention site there, not in so many words," Wilkerson said. "What they indicated is that interrogations took place there."

His sources did not tell him that there was a purpose-built facility on the atoll, the 70-year-old said.

"What I heard was more along the lines of using it as a transit location when perhaps other places were full or other places were deemed too dangerous or insecure, or unavailable at the moment. So you might have a case where you simply go in and use a facility at Diego Garcia for a month, or two weeks, or whatever, and you do your nefarious activities there."

It is the first time a senior Bush administration official has stated on the record that the remote British territory was a part of the CIA's global network of black sites. The US has operated a military base on the atoll since the British leased it to them in the 1960s.

The disclosures will renew questions over the extent to which the British were aware of Diego Garcia's function in the US's post-9/11 extraordinary rendition program.

Wilkerson, a 31-year army veteran who knows Diego Garcia from his time in the US Pacific Command in the 1980s, said he thought it unlikely that the small number of British military present on the island would have missed the arrival and departure of detainees.

"It's difficult for me to think that we could do anything there of any duration to speak of without the British knowing — at least the British on the island — knowing what we were doing," he said.

"That doesn't mean London knew," he added. "But I just don't, myself, I can't see how we could have used Diego Garcia for almost any function other than maybe a bounce-in and bounce-out and even that, the bounce-in and bounce-out, they'd be aware of."

The question of British cooperation is an extremely sensitive one for the British government, which has sought to distance itself from any suggestion of complicity in the US's post-9/11 rendition and torture program. Confirmation that the British were involved could leave the government vulnerable to legal action. The European Court of Human Rights made its first ruling on the CIA's secret prisons in Europe last year when it found that detainees had been held and tortured in Poland.

Last year Al Jazeera America reported that the Senate Intelligence Committee report on CIA torture would confirm that Diego Garcia was used for extraordinary rendition "with the full cooperation" of the UK — but the heavily redacted document was published months later with no mention of the atoll.

In September former Attorney General Lord Goldsmith told VICE News that he had "no recollection" of whether discussions were had over the legality of using Diego Garcia as a black site during his tenure as most senior legal advisor to Tony Blair.

Previous disclosures by British military personnel have dismissed the construction of a purpose-built detention facility on the island as a logistical impossibility. They have not ruled out the possibility that Diego Garcia could have been used as a temporary holding facility, however.

Testimony filed in the high court by a British Royal Marine, Michael Blyth, who was head of security on Diego Garcia from 2001-2, said that a permanent site was ruled out but the use of the atoll "for the purpose of prisoner transfers and/or detention was raised occasionally ... by US official." Blyth said he thought it was unlikely but possible that detainees in planes may have gone unnoticed by the British in the busy years after 9/11 when "scores of planes took off daily."

"Could somebody convert a room within the airbase and sneak one or two people in, beat them up and take them out again?" Blyth told the Telegraph last year. "Yes, I suppose so, if you did it in the dead of night and you only did it a couple of times.

"But eventually someone would spot it and the rumours would get out of control and everyone would hear about it. I suspect it wouldn't be a good option. There were much better options to transfer through than Diego," he said.

The British government has said that only two rendition flights stopped over at Diego Garcia to refuel, both in 2002. Manfred Nowak, the United Nations' former special rapporteur on torture, told the Observer in 2008 that sources had told him detainees were held on Diego Garcia between 2002-3. A former US general, Barry McCaffrey, also said Diego Garcia held detainees — but later retracted the claim. Libyan politician Abdel Hakim Belhaj, who believes he was rendered through Diego Garcia when he was abducted in a joint MI6-CIA operation, is currently suing the UK government over his kidnap.

Flight records for the atoll that may hold crucial details of the extraordinary rendition flights that passed through Diego Garcia are incomplete and may be water damaged, according to the British government.

Cori Crider, a director at human rights NGO Reprieve said: "This suggests the UK Government has not told the whole truth about Diego Garcia's part in the CIA's torture program.

"Ministers have consistently claimed that only two CIA rendition victims ever landed on Diego Garcia — Lawrence Wilkerson's comments suggest that either they haven't been honest with the public, or the US government hasn't been honest with them. These revelations will also cast suspicion over the British government's ongoing refusal to publish flight records for the island. Until we can get a straight answer from the US and UK government on what went on on Diego Garcia, there should be no renewal of the US lease, which is due to expire next year."

A UK Foreign Office spokesperson said: "The US government has assured us, that apart from the two cases in 2002, there have been no other instances in which US intelligence flights landed in the UK, our Overseas Territories, or the Crown Dependencies with a detainee on board since 11 September 2001."

A CIA spokesperson said: "We have no comment for you."