Current U.S. detection methods would likely have spotted the shape of the explosive in the upgraded underwear bomb intercepted by the CIA, said a U.S. official speaking on condition of anonymity to discuss security precautions. No new security measures are being put in place, the official said.
The CIA, with help from a well-placed informant and foreign intelligence services, conducted a covert operation in Yemen in recent weeks that disrupted a nascent suicide plot and recovered the new bomb, U.S. officials said.
Officials said the bomb has a more refined detonation system than the underwear bomb that failed to go off aboard a jetliner over Detroit on Christmas 2009.
FBI experts are picking apart that non-metallic device to see if it could have taken down an airplane.
Some passengers, meanwhile, were taking the news of the new bomb in stride.
"The terrorists will always be looking to make a bomb," said Guillaume Viard, a 26-year-old physiotherapist from Nice, France, about to board a flight to Paris at New York's John F. Kennedy Airport.
Retirees Nan and Bill Gartner, also at Kennedy Airport, were on their way to a vacation in Italy
"We were nervous - for a minute," said Nan Gartner. "But then we thought, we aren't going anywhere near Yemen, so we're OK."
Added Bill Gartner, "We hope we're right."
U.S. officials are trying to reassure the public that security measures are strong, and can frustrate such attacks.
"I think people getting on a plane today should feel confident that their intelligence services are working, day in and day out," John Brennan, the top counterterrorism adviser to President Barack Obama, said on ABC's "Good Morning America."
Just last winter, al-Qaida's Yemen branch boasted that it had obtained a supply of chemicals used to make bombs. Chemicals can eliminate the need for electrical equipment to detonate explosives.
"Hence, no wearisome measures are taken anymore to attain the needed large amount of chemicals for explosives," the group wrote in its online magazine, "Inspire."
Working with an informant close to al-Qaida in Yemen, the CIA caught wind of the bomb plot last month, officials said, speaking on condition of anonymity to discuss intelligence matters.
The would-be bomber was supposed to buy a plane ticket to the United States and detonate the bomb inside the country, officials said.
Sen. Dianne Feinstein, D-Calif., who heads the Senate Intelligence Committee, told reporters Monday night that she had been briefed about an "undetectable" device that was "going to be on a U.S.-bound airliner."
Before the bomber could choose his target or buy his ticket, however, the CIA swooped in and seized the bomb.
The fate of the would-be bomber remains unclear. Rep. Peter King, R-N.Y., chairman of the House Homeland Security Committee, told CNN on Tuesday that White House officials told him "He is no longer of concern," a point Brennan echoed on a round of appearances Tuesday on television news shows.
"We're confident that this device and any individual that might have been designed to use it are no longer a threat to the American people," Brennan said.
The plot was a reminder of the ambitions of al-Qaida in Yemen, the most active and dangerous branch of the terrorist group. While al-Qaida's core in Pakistan has been weakened over the past decade, instability in Yemen has allowed an offshoot group to thrive and set up training camps there. In some parts of the country, al-Qaida is even the de facto government.
Though analysis of the device is incomplete, U.S. security officials said they remained confident in the security systems in place.
"These layers include threat and vulnerability analysis, prescreening and screening of passengers, using the best available technology, random searches at airports, federal air marshal coverage and additional security measures both seen and unseen," Department of Homeland Security spokesman Matthew Chandler said.
"The device did not appear to pose a threat to the public air service, but the plot itself indicates that these terrorist keep trying to devise more and more perverse and terrible ways to kill innocent people," Secretary of State Hillary Rodham Clinton said during a news conference in New Delhi with Indian External Affairs Minister S.M. Krishna.
It's not clear who built the bomb, but because of its sophistication and its similarity to the Christmas Day bomb, authorities suspected it was the work of master bomb maker Ibrahim Hassan al-Asiri or one of his students. Al-Asiri constructed the first underwear bomb and two others that al-Qaida built into printer cartridges and shipped to the U.S. on cargo planes in 2010.
Both of those bombs used a powerful industrial explosive. Both were nearly successful.
But the group has also suffered significant setbacks as the CIA and the U.S. military focus more on Yemen. On Sunday, Fahd al-Quso, a senior al-Qaida leader, was killed by a missile as he stepped out of his vehicle along with another operative in the southern Shabwa province of Yemen.
Al-Quso, 37, was on the FBI's most wanted list, indicted in the U.S. for his role in the 2000 bombing of the USS Cole in the harbor of Aden, Yemen, in which 17 American sailors were killed and 39 injured.
Al-Quso was believed to have replaced Anwar al-Awlaki as the group's head of external operations. Al-Awlaki was killed in a U.S. airstrike last year.
Al-Quso told a Yemeni journalist in February that AQAP's recent focus on defeating Yemeni forces did not mean the group had abandoned attacks on the U.S.
"The war didn't end between us and our enemies," al-Quso said. "Wait for what is coming."
The new Yemeni president, Abed Rabbo Mansour Hadi, has promised improved cooperation with the U.S. to combat the militants.
On Tuesday, Pentagon spokesman Navy Capt. John Kirby confirmed more U.S. trainers are being dispatched to Yemen for "routine" cooperation with Yemeni security forces. A second U.S. official said they are special operations troops.
A U.S. Navy SEAL-led task force based in the region has worked with Yemeni counterterrorist teams since roughly 2009.
Associated Press writers Matt Apuzzo, Adam Goldman, Ted Bridis, Bob Burns and Alan Fram in Washington; Verena Dobnik in New York, oand Matthew Lee in New Delhi contributed to this report.