President Obama was made aware of the threat in April, U.S. officials said, and the plot was stopped before any aircraft or passengers could be put in danger. Obama "was assured that the device did not pose a threat to the public," said Caitlin Hayden, a spokeswoman for the National Security Council.
U.S. officials said the FBI is examining the device - modeled on the "underwear bomb" used in an attempt to bring down a Detroit-bound airliner on Christmas Day 2009 - to determine whether airport security systems would have detected it.
U.S. officials said the CIA and other agencies tracked the plot
Officials said that the bomb or its components were in transit when intercepted, but that the device was not seized at an airport and that al-Qaeda had yet to target a specific flight, let alone take steps to smuggle the explosive onboard.
U.S. officials declined to provide key details about the plot, citing concern about protecting sensitive intelligence sources and operations
The timing of the alleged terrorist plot coincides with a major escalation of the clandestine U.S. drone campaign in Yemen. U.S. officials said the explosive appears to have been assembled by al-Qaeda in the Arabian Peninsula, or AQAP, a Yemen-based affiliate that has been linked to high-profile attacks against the United States.
In addition to the 2009 airliner bombing plot, AQAP has been tied to an unsuccessful 2010 attempt to mail parcels packed with explosives to addresses in Chicago and a 2009 attack in Saudi Arabia in which a suicide bomber was killed during a gruesome attempt to assassinate the kingdom's top counterterrorism official, Mohammed bin Nayef.
Bomb 'difficult to detect'
U.S. officials said the new device was designed to overcome technical problems and detection schemes that had thwarted previous AQAP plans. The bomb was built with a more advanced detonator than the one that fizzled during the foiled Christmas Day attack, in which the would-be bomber, Omar Farouk Abdulmutallab, was subdued by other passengers alarmed by plumes of smoke rising from his seat.
The new device was also devoid of metal or telltale components, meaning that it might have been difficult for any but the most sophisticated airport security systems to detect.
Sen. Dianne Feinstein (D-Calif.), chairman of the Senate Select Committee on Intelligence, described the device as "a specific type of bomb that is of new design and very difficult to detect by magnetometer."
In a written statement, she said, "It was similar to what . . . Abdulmutallab wore in his underwear."
That device and others are thought to be the work of Ibrahim Hassan al-Asiri, an accomplished AQAP-affiliated bombmaker who remains at large.
Bin Laden anniversary
The disclosure of the plot, first reported by the Associated Press, comes less than a week after the anniversary of the death of Osama bin Laden and amid recent efforts by the Obama administration to make its counterterrorism accomplishments a central issue in the presidential campaign.
White House officials previously said they were unaware of any terrorism plots tied to the one-year mark of bin Laden's death. Despite Monday's disclosure, a senior administration official said those assertions were accurate.
"We had no specific, credible information about active terrorist plots timed to coincide with the bin Laden anniversary and reiterate that this device never represented a threat to the public," the senior official said.
Nevertheless, the detection of the alleged al-Qaeda plan appears to have set a series of counterterrorism operations in motion.
Last month, Obama approved a significant escalation of the drone campaign in Yemen, allowing the CIA and the U.S. Joint Special Operations Command to begin firing at targets engaged in activity deemed suspicious, even when the identities of those who could be killed is unknown.
Fahd al-Quso, a senior AQAP operative reportedly killed in the latest drone strike, was said to have succeeded the U.S.-born Anwar al-Awlaki as AQAP's head of external planning. Awlaki was killed in a CIA drone attack last year.
Quso was tied to the 2000 attack on the USS Cole in Yemen that killed 17 American sailors. U.S. officials said he was likely to have been involved in any plot to strike the United States. Officials declined to say whether he was targeted based on intelligence gathered when the bomb was intercepted.
AQAP threat 'growing'
CIA analysts have warned administration officials in recent months that AQAP's ability to seize large chunks of territory in Yemen over the past year has made it more dangerous to the United States and its Western allies.
"It is our assessment that the threat from AQAP is growing due to the territorial gains," the senior U.S. official said, adding that its territorial expansion has "allowed the group to establish additional training camps."
U.S. officials did not say whether the seizure of the latest bomb had triggered specific security precautions. The FBI said in a statement that the device was "seized abroad" but that the bureau "has possession of [it] and is conducting technical and forensics analysis."