The suicide bomber dispatched by the Yemen branch of Al Qaeda last month to blow up a United States-bound airliner was actually an intelligence agent for Saudi Arabia who infiltrated the terrorist group and volunteered for the mission, American and foreign officials said Tuesday. In an extraordinary intelligence coup, the double agent left Yemen last month, traveling by way of the United Arab Emirates, and delivered both the innovative bomb designed for his aviation attack and inside information on the group’s leaders, locations, methods and plans to the Central Intelligence Agency, Saudi intelligence and allied foreign intelligence agencies. Officials said the agent, whose identity they would not disclose, works for the Saudi intelligence service, which has cooperated closely with the C.I.A. for several years against the terrorist group in Yemen. He operated in Yemen with the full knowledge of the C.I.A. but not under its direct supervision, the officials said. After spending weeks at the center of Al Qaeda’s most dangerous affiliate, the intelligence agent provided critical information that permitted the C.I.A. to direct the drone strike on Sunday that killed Fahd Mohammed Ahmed al-Quso, the group’s external operations director and a suspect in the bombing of the U.S.S. Cole, an American destroyer, in Yemen in 2000. He also handed over the bomb, designed by the group’s top explosives expert to be undetectable at airport security checks, to the F.B.I., which is analyzing its properties at its laboratory at Quantico, Va. The agent is now safe in Saudi Arabia, officials said. The bombing plot was kept secret for weeks by the C.I.A. and other agencies because they feared retaliation against the agent and his family — not, as some commentators have suggested, because the Obama administration wanted to schedule an announcement of the foiled plot, American officials said. Officials said Tuesday night that the risk to the agent and his relatives had now been “mitigated,” evidently by moving both him and his family to safe locations. But American intelligence officials were angry about the disclosure of the Qaeda plot, first reported Monday by The Associated Press, which had held the story for several days at the request of the C.I.A. They feared the leak would discourage foreign intelligence services from cooperating with the United States on risky missions in the future, said Representative Peter T. King, a New York Republican and chairman of the House Homeland Security Committee. “We are talking about compromising methods and sources and causing our partners to be leery about working with us,” said Mr. King, who spoke with reporters about the plot on Monday night and Tuesday after he was briefed by counterterrorism officials. Mr. King, who called the bomb plot “one of the most tightly held operations I’ve seen in my years in the House,” said he was told that government officials planned to investigate the source of the original leak. The C.I.A. declined to comment. Intelligence officials believe that the explosive is the latest effort of the group’s skilled bomb maker, Ibrahim Hassan al-Asiri. Mr. Asiri is also believed to have designed the explosives used in the failed bombing attempt on an airliner over Detroit on Dec. 25, 2009, and packed into printer cartridges and placed on cargo planes in October 2010. A senior American official said the new device was sewn into “custom-fit” underwear and would have been very hard to detect even in a careful pat-down. Unlike the device used in the unsuccessful 2009 attack, this bomb could be detonated in two ways, in case one failed, the official said. The main charge was a high-grade military explosive that “undoubtedly would have brought down an aircraft,” the official said. Forensic experts at the F.B.I.’s bomb laboratory are assessing whether the bomb could have evaded screening machines and security measures revamped after the failed 2009 plot. One American official said the bureau’s initial analysis indicated that if updated security protocols designed to detect a wider range of possible threats were properly conducted, the measures “most likely would have detected” the device. On Tuesday, the Transportation Security Administration repeated a security message previously sent to airlines and foreign governments. The security guidance notes that Al Qaeda in the Arabian Peninsula still intends to attack the United States, probably using commercial aviation, and warns T.S.A. agents to look out for explosives in cargo, concealed in clothing or surgically implanted, officials said. Over the past eight months, American counterterrorism officials have monitored with growing alarm a rising number of electronic intercepts and tips from informants suggesting that Al Qaeda’s branch in Yemen has been ramping up plots to attack the United States. “There was increasing concern about the chatter, more and more intelligence” that Al Qaeda in the Arabian Peninsula “was moving with renewed energy to carry out some kind of attack against homeland, using airliners and concealed explosives,” said one senior administration official. Working with foreign allies, the Obama administration quietly tightened airport security. The ominous signs followed months of political chaos in Yemen during which the Qaeda branch and its militant allies seized effective control over large areas of the country, giving the terrorist group a broader base from which to plot attacks against both the Yemeni government and the United States. Senior American counterterrorism and military officials have expressed concern that Al Qaeda’s growing number of training camps, including small compounds, have churned out dozens of new fighters who, in turn, help expand the area under the insurgents’ control. Officials fear that the camps could also train Qaeda operatives for external operations against targets in Europe and the United States. “Certainly when they hold terrain, it makes training more safe and secure than on disputed terrain; therefore, more and better training,” said one senior American military official. The Yemeni government’s control over the hinterlands southeast of the capital, Sana, has always been tenuous, but over the past year it has receded almost entirely. With the authorities focused on political turmoil in the capital, many soldiers fled their posts, and jihadists began asserting control. For more than a year the town of Jaar — along with several smaller settlements — has been controlled by militants who operate under the banner Ansar al-Sharia, which is variously described as a wing of Al Qaeda’s Yemeni branch or as an allied group. One prominent tribal mediator from Shabwa Province, reached Tuesday by phone, said Ansar al-Sharia controlled all the checkpoints on Yemen’s southern coast between Aden and Balhaf, and as far north as Ataq. On Monday, militants attacked several army bases and outposts in the south, killing 20 soldiers and capturing 25, The Associated Press reported. Local tribal figures described the attacks as revenge for the killing of Mr. Quso on Sunday. Control in the south often appears to be shared between militants, local tribes and members of the southern independence movement, which is largely secular. But Qaeda militants and their allies appear to operate freely even in areas they do not fully control, possibly including Aden, the south’s major city. Aden has become a bastion of open opposition to the government, with the flag of the independence movement — once rigidly banned — now flying from houses across the city. _________________________ Scott Shane and Eric Schmitt, "Bomber in Plot on U.S. Airliner Is Said to Be a Double Agent," The New York Times, May 8, 2012, http://www.nytimes.com/2012/05/09/world/middleeast/suicide-mission-volunteer-was-double-agent-officials-say.html.