By William Maclean
LONDON, May 11 (Reuters) - Counter-terrorism experts expressed concern on Friday over U.S. leaks about an undercover operation that foiled a suicide bomb plot, saying its exposure may deter agents from volunteering for the risky job of infiltrating al Qaeda's network.
While electronic methods are increasingly used in espionage operations of all kinds, human intelligence remains crucial because al Qaeda's best operatives try to avoid the use of any electronic communications to minimise the chance of detection.
British intelligence played a central role in the operation targeting al Qaeda's Yemeni offshoot, counter-terrorism sources told Reuters, by recruiting the informant who obtained the bomb and handed it to Western intelligence officers.
The undercover operative in the plot linked to Al Qaeda in the Arabian Peninsula, or AQAP, was a British citizen, possibly of Saudi origin, the sources said on condition of anonymity. The informant was working in cooperation with Britain's two principal spy agencies.
The operation appears to have been a joint venture between the British, Saudi Arabian and U.S. intelligence services, some analysts say, and its exposure in the U.S. media has caused widespread concern in the U.S. intelligence community.
The Saudis and British appear to be concerned too.
"The Saudis are not happy with the leaking of this information," said Mustafa Alani, a security analyst with good contacts among Gulf Arab governments.
"It is potentially harmful for future operations. And it is the Saudis who have the agents on the ground to get these things done."
A spokesman for Prime Minister David Cameron declined to discuss the matter, but said: "Clearly we think that sensitive information should be protected."
Nigel Inkster, a former assistant chief of Britain's Secret Intelligence Service (SIS), said in a Twitter message: "The revelations about the British agent in AQ (al Qaeda) remind us that Beltway leaking is a major security threat."
Patrick Mercer, a British Conservative Party lawmaker and a specialist in security matters, said: "If this is not a deliberate disclosure done for an operational purpose, then it is a shocking example of a leak posing risks to highly sensitive and important work."
The operation appears to have been a notable counter-terrorism success for the United States and its allies, with the adroit use of an agent inside al Qaeda ranks likely to provide particular satisfaction to Washington two and a half years after the second most deadly attack on the Central Intelligence Agency (CIA).
On Dec. 30 2009, a Jordanian double agent, Humam Khalil abu Mulal al-Balawi, blew himself up inside Forward Operating Base Chapman, a well-fortified U.S. compound in Khost province in southeast Afghanistan, killing seven CIA officers and a Jordanian intelligence officer.
The attack showed militants were keener to kill Western spies than to infiltrate their networks, underlining the daunting challenge for Western services seeking to plant an informant among al Qaeda's senior ranks.
And yet the disclosure of the latest operation may make it less likely that others will come forward to undertake such undercover work against al Qaeda in future, analysts say.
In the latest case, Alani said AQAP had been duped into recruiting the informant because, among other things, he held a Western passport and appeared to have a militant cast of mind, making it easier for him to be allowed to board a U.S.-bound plane without undue suspicion.
But by definition individuals who have the temperament, background and training to infiltrate the militant network are few.
This is not the first time such leaks have disrupted operations involving British and Saudi intelligence.
The most notable case where U.S. leaks potentially jeopardised a British investigation was that of an al Qaeda plot to blow up financial targets in the United States and carry out "dirty bomb" attacks in Britain.
The eight-man cell, now serving long jail terms, were arrested in daylight swoops by British police in 2004 after U.S. officials revealed details about a Pakistani agent who was involved in a sting operation.
The men had been under police surveillance and the release of the Pakistan agent's name in U.S. newspapers prompted the British to act faster than they wanted.
Security analysts say British police were also forced to arrest suspects believed to be planning to down transatlantic airliners in 2006 earlier than they had wanted because U.S. security agencies were putting them under pressure.
A lack of evidence meant the suspects were not initially convicted of being involved in planning to target airliners and led to a number of re-trials.
In a speech in 2010, SIS chief John Sawers said: "Agents take serious risks and make sacrifices to help our country. In return, we give them a solemn pledge: that we shall keep their role secret."
Secret organisations needed to stay secret, he said, even if they occasionally presented "a public face".
"Agents take risks. They will not work with SIS, will not pass us the secrets they hold, unless they can trust us not to expose them. Foreign partners need to have certainty that what they tell us will remain secret - not just most of the time, but always."
The director of U.S. National Intelligence has opened an "internal review" of U.S. intelligence agencies to determine whether there were leaks of classified information related to the underwear bomb operation.
Separately, the FBI is conducting a separate criminal investigation into leaks, a law enforcement official said in Washington. (Additional reporting by Michael Holden and Mark Hosenball in Washington; Editing by Andrew Osborn)