A man who al-Qaeda hoped would carry out a plot to blow up a U.S.-bound airliner is a mole who infiltrated the terrorist organization and thwarted the attack, U.S. and Yemeni officials said Tuesday.

The secret operative — working for CIA and Saudi intelligence handlers in Yemen — provided the U.S. with key information on a nearly undetectable bomb that al-Qaeda hoped would destroy a plane and usher in a new era of terror, the Associated Press reported.

The officials spoke on condition of anonymity because of the sensitivity of the operation, the AP said. The plot was foiled in the early stages.

• STORY: Second underwear bomb plot thwarted

The U.S. military recently sent "trainers" to Yemen to help them deal with al-Qaeda, which has been causing instability in the country, said U.S. Navy Capt. John Kirby, deputy assistant secretary of Defense. He wouldn't reveal the nature of the operations.

"We have been working with the government of Yemen … for some time now to help them deal with the growing al-Qaeda threat inside Yemen," Kirby said.

Michael Chertoff, the former secretary of Homeland Security, expects more plots from South Asia and Yemen, perhaps with liquid explosives. The latest plot didn't prompt a significant overhaul in security, meaning the bomb was probably not a threat to current screening.

Nevertheless, "we have to continue to adapt," Chertoff said.

The FBI is analyzing the explosive, which was intended to be concealed in a passenger's underwear. Officials said it was more sophisticated than the bomb that failed to detonate on board an airplane over Detroit on Christmas 2009.

The new bomb contained no metal and used a chemical — lead azide — that was to be a detonator in a nearly successful 2010 plot to attack cargo planes, officials said.

The latest underwear bomb was aimed at a potential gap in security technology, which experts say reinforces the importance of blending intelligence gathering with airport screening.

Full-body scanners are deployed at 170 airports across the USA to find non-metallic explosives that metal detectors miss, such as the bomb the CIA discovered recently in Yemen.

The scanners aren't always available, and security experts aren't clear about whether they would have caught the latest bomb.

Even if the scanning machines work, airports overseas have been slower to adopt them because of privacy concerns, concerns in Europe about radiation from X-rays and cultural differences in the Middle East. That's what makes intelligence gathering key to finding bombs before they reach the airport.

Terrorist organizations are " looking for the weakest link in the chain," said Rich Cooper, a fellow at George Washington University's Homeland Security Policy Institute.

"You have to look at security as a series of layers," Chertoff added. "No one layer is flawless or foolproof."

http://www.usatoday.com/news/world/story/2012-05-08/qaeda-bomb-plot-cia/54843854/1