A British citizen played a central role in foiling the latest "underwear" bomb plot hatched in Yemen to attack a US-bound plane, as well as in the assassination of a top al-Qaida operative at the weekend, according to various sources in Washington on Thursday.
CNN reported that the agent involved was a British citizen of Saudi origin who had been recruited about a year ago by Saudi intelligence.
MSNBC, which also reported that the agent was a British passport holder, said that British intelligence was "heavily involved". Other US media outlets gave the Saudi intelligence service most of the credit for the successful running of the operation. The Guardian independently confirmed British involvement.
The agent was recruited by al-Qaida in the Arabian Peninsula (AQAP), which operates in Yemen and Saudi Arabia, and asked to carry a bomb aboard a US-bound plane.
The revelation is politically and legally awkward for MI6 and MI5 whose agents, unlike American ones, are banned from missions that lead to assassinations, such as the US drone attack at the weekend that killed the top al-Qaida operative in the Yemen, Fahd al-Quso. The attack is being attributed to information from the agent.
Such is the sensitivity that America's National Public Radio reported that the British government asked the Obama administration not to reveal the role of British intelligence in the mission.
James Clapper, the US director of National Intelligence, has opened an "internal review" of US intelligence agencies to determine whether there had been leaks of classified information related to the underwear bomb operation.
The FBI is conducting a separate criminal investigation, a law enforcement official said. The US defence secretary, Leon Panetta, a former CIA director, said: "When these leaks take place, they damage our ability to be able to pursue our intelligence efforts."
The agent has not yet been identified but, according to US officials, he was recruited by al-Qaida in the Yemen and given a bomb similar to – but more sophisticated than – the one used by Umar Farouk Abdulmutallab, who was jailed this year for a failed attempt to bring down a plane over Detroit in 2009. That plot also originated in Yemen.
The agent involved in the latest attempt took the bomb and then handed it over. It is now being examined by the FBI at its laboratories in Quantico, Virginia.
The Washington Post reported that the agent was one of several sent into Yemen over the past two years with western passports and other documents designed to attract the attention of al-Qaida.
It is unusual for the US to brief in this way about the internal workings of other intelligence services. It may be that the CIA did not want to be falsely credited with the success in foiling the plot.
The Associated Press learned about the plot last week, but held off reporting it as the request of the White House for what were cited as operational reasons. AP finally reported the story on Monday, the day after the assassination of Quso.
On Wednesday, the US reported that the would-be bomber had been an agent.
The White House declined to confirm or deny British involvement, citing operational sensitivities. A spokesman for the British embassy said: "We do not comment on intelligence matters."
In the past, British intelligence might have been happy to have taken credit for what is being hailed in the US as a major intelligence coup. But not this time.
British officials in London referred all questions from the media to the US.
Their reluctance to comment may be because of the rule that Britain's security and intelligence agencies are not allowed to task their agents for operations deliberately designed to lead to the death of an individual. MI6 was banned in the 1960s from any involvement in assassination plots.
But, according to US officials, the double-agent's mission was to find the bombmaker for AQAP, Ibrahim Hassan al-Asiri, and pass on the location to the US. Over the past month, the CIA has sought and received permission to expand drone attacks in the Yemen.
The disclosure in the US of the plot comes at a bad time for MI6. Its officers are being investigated by the police over the rendition of Libyan dissidents to Muammar Gaddafi's secret police who, the dissidents say, tortured them.
When the US government confirmed the AP story on Monday, it acknowledged the plot had been foiled with the help of other intelligence agencies, without specifying which ones. It has since emerged that the Saudi intelligence service as well as British intelligence was involved.
The British agent would have been attractive to al-Qaida as a bomb-carrier. Al-Qaida has long welcomed sympathisers with western passports, seeing them as more capable of getting through airport security. The agent failed to discover the whereabouts of Asiri. But Quso was killed by the drone attack on the car he was travelling in Shabwa province in Yemen.
Yemen has been the source of several attempts to target the US, including the successful attack on the USS Cole.
On Monday, the Republican Congressman Peter King, chairman of the House homeland security committee and is regularly briefed by the intelligence services and the White House , said he was told by the White House that the intelligence operation and the targeting of al-Quso were connected.
According to CNN, the agent was accepted for training as a suicide bomber and then contacted Saudi intelligence, who in turn informed the US.
How plot unravelled
April According to US officials, al-Qaida in the Arabian Peninsula hatched a plot to bomb a US-bound plane using a more sophisticated device than that used in the failed 2009 "underwear" bomb attempt on a plane over Detroit.
Last week AP learned about the failed plot but held back its report at the request of the White House.
Sunday A CIA drone attack in Yemen killed a a senior al-Qaida operative, Fahd al-Quso.
Monday AP ran its story and the White House confirmed it. But there were no details published about the identity or whereabouts of the would-be bomber. A congressman, Pete King, said the same intelligence operation involved not only stopping the bombing but had identified the whereabouts of al-Quso.
Tuesday The US revealsed the would-be bomber was in fact an agent who had infiltrated al-Qaida pretending to be a volunteer for a sucide mission. It is being taken apart by an FBI forensics team.
Thursday Another twist. Various US sources revealed the agent was a British citizen of Saudi origin.
