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US Defence Secretary Leon Panetta has said he fully supports plans by the US Government's Director of National Intelligence to investigate how the US media found out that the 'double agent' who helped foil al-Qaeda's underwear bomb was a British citizen.
He said the leak was "harmful" to the intelligence community.
The US Defence Secretary Leon Panetta has said the leaks to the press about the identity of the undercover agent who foiled an al-Qaeda plot to blow up an underwear bomb were dangerous, and would be investigated.
Speaking to reporters at a press briefing at the Pentagon he said:
"The whole effort is to be able to try to get individuals who can provide intelligence and work with us, and to be able to do that, and to do that effectively you have to be able to protect these people"
"When these leaks take place, I can't tell you how much they damage our ability to be able to pursue our intelligence efforts"
The undercover informant in the foiled underwear bomb plot linked to al Qaeda's Yemeni affiliate was a British citizen, possibly of Saudi origin, US counter-terrorism officials said.
British intelligence played a central role in the operation that foiled the plot to send a suicide bomber onto an airplane, and it was a cooperative effort between MI5 and MI6, Britain's domestic and foreign intelligence services known, officials told Reuters on condition of anonymity.
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.
US and Yemeni officials have confirmed that the would-be bomber at the heart of an al-Qaida airliner plot was actually a double agent working for the CIA and Saudi intelligence.
The FBI is still analysing the explosive, which was intended to be concealed in a passenger's underwear.
The latest underwear bomb plot was uncovered by a CIA under-cover agent according to the New York Times.
It is claimed that the agent volunteered to infiltrate the terrorist group and was able to supply vital operational information and take delivery of the bomb before delivering it safely in to the hands of U.S. officials.
US sources have told NBC News that British intelligence was "heavily involved" and "very critical" in the thwarting of a bomb plot against US airliners.
Publicly a senior US counter terrorism official said only that multiple friendly security services were involved in the operation.
US congressional and security officials have suggested that there is no immediate need to change airport security procedures, despite the discovery of a sophisticated new al Qaeda airline bomb plot.
US security officials said they remained confident in the security systems that were in place. Department of Homeland Security spokesman Matthew Chandler said:
"These layers include threat and vulnerability analysis, pre-screening and screening of passengers, using the best available technology, random searches at airports, federal air marshal coverage and additional security measures both seen and unseen".
Latest ITV News reports
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.