The man who foiled a Yemen-based al-Qaeda "underwear bomb" plot is reported to have been a British man of Middle Eastern origin, according to US media.
UK officials declined to comment on the reports, but earlier this week the US said foreign agencies were involved in the operation.
The agent was sent by al-Qaeda to attack a US-bound plane, but left Yemen and gave the device to US intelligence.
The US insists the bomb never posed a threat to the public.
Western passport-holders have long been seen as prime targets for militant groups seeking to plan attacks.
However, as well as reporting that the secret agent was a British citizen, NBC News in the US also says UK intelligence agencies were "heavily involved" in his recruitment.
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