British intelligence played a central role in the undercover investigation to foil an underwear bomb plot involving al Qaeda's Yemeni offshoot, sources told the Reuters news agency.
The Obama administration had been under heavy pressure not to disclose the role of British authorities in the investigation.
The foiled plot ended with the explosive device in the hands of the FBI, which is examining it.
An undercover agent who foiled an al-Qaeda plot to blow up an airliner with an underwear bomb is a British national.
It seems the man who foiled al-Qaeda's latest underpants bombing plot was a Saudi intelligence agent.
Ibrahim Hassan al-Asiri is the man the FBI think is behind the latest al-Qaeda terror threat to come out of Yemen.