Yemen terror group may have made more underwear bombs, US officials say The man at the center of the alleged al-Qaida terror plot to bring down a passenger airliner headed to the United States was a double agent cooperating with the U.S. NBC's Pete Williams reports. Just days before the news broke about the CIA's takedown of a plot involving a sophisticated new underwear bomb, al-Qaida's affiliate in Yemen publicly boasted that it had vastly expanded and improved its capabilities for making such devices. That boast -- contained in a largely overlooked passage of Inspire, the online propaganda organ of al-Qaida in the Arabian Peninsula (AQAP) -- has fueled concerns that there may be other versions of the seized device and more bomb makers assembling them, according to U.S. security officials and members of Congress who have been briefed on the case. They have a team of engineers, scientists and doctors. It's a little spooky," said Rep. Mike McCaul, R-Texas, a member of the Homeland Security Committee who was briefed this week on the intelligence operation that U.S. officials say thwarted an AQAP plot to bomb a U.S.-bound airliner. In my view, it's very likely they have produced more of these. One hint at the expansion of AQAP's bomb-making capabilities can be found in passages in an article entitled "Wining on the Ground," found on the 57th page of the latest 59-page edition of Inspire, released by AQAP last weekend. In 2009, AQAP had only a "very modest and small laboratory in a rural area" to make bombs, the author of the article -identified as Yahya Ibrahim -- wrote. Michael Leiter, former director of the National Counterterrorism Center, talks to TODAY's Ann Curry about the dangers of revealing too much information about how the U.S. and its allies foiled the alleged al-Qaida plot to bomb a passenger airliner. That was the year AQAP dispatched a suicide bomber to use a chemical underwear bomb to attempt to assassinate Prince Mohammed bin Nayef bin Abdul Azizbin, director of Saudi Arabia's counterterrorism program, and later deployed another operative from Nigeria to try to blow up a U.S. airliner bound for Detroit. Neither device detonated properly, though the bomber in the first attack was killed. But now, after obtaining "a large deal of chemicals from military laboratories" in a key city in southern Yemen -- "the modest lab has transformed into a modern one," the Inspire article stated. "Hence, no wearisome measures are taken anymore to obtain the needed large amount of chemicals for explosives," it said. Also, the operations now do not lack money as before. Insider who thwarted bomb plot was supposed to carry it out This was not the first time AQAP has signaled that its bomb-making capabilities may be greater than U.S. officials have suggested. In an issue of Inspire in late 2010, the group appeared to mock comments by U.S. officials focusing on the critical role of its top bomb-maker, Ibrahim Hassan Asiri -- who has been widely credited with designing the underwear bombs. "Isn't it funny how America thinks AQAP has only one major bomb maker?" an article stated. Gregory Johnsen, a highly respected Yemen scholar who specializes in AQAP at Princeton University, said the propaganda outlet's statements are likely true. "We have to assume that there is not only one bomb-maker," he said. "It makes sense that he (Asiri) is somebody who has taught others" about making such bombs. Johnsen said that the expansion of AQAP's bomb-making operations would be just one example of the dramatic gains the group has made in the past few years. As a result of the internal chaos in Yemen, and its shrewd exploitation of civilian casualties caused by U.S. air strikes, AQAP has made major advances, Johnsen said. By U.S. intelligence estimates, the number of AQAP fighters has tripled to more than 1,000. It has also seized swaths of territory in southern Yemen, where it runs its own court system, deploys police officers and provides electricity to some towns, Johnsen said. U.S. intelligence officials say they have no specific information indicating that other improvised explosive devices (IEDs) similar to the one that was turned over by a CIA informant last month have been produced and possibly spirited out of Yemen. But John Brennan, President Barack Obama's chief counterterrorism adviser, said Tuesday in an interview with PBS that U.S. officials are taking additional measures "to prevent any other type of IED similarly constructed from getting through security procedures." At the same time, the U.S. Department of Homeland Security issued new "guidance" calling for enhanced security at foreign airports, including additional pat-downs and random searches, as well as other steps aimed at detecting such bombs.