WASHINGTON — American counterterrorism forces recently thwarted an apparent plot to bring down a commercial plane, seizing a new, more sophisticated explosive device designed to be worn by a passenger, government officials said Monday.
Officials said the plot had been based in Yemen and appeared to be a second attempt at the kind of attack that failed in 2009 when a passenger on a flight to Detroit tried to set off an explosive hidden in his garments.
The explosive, which contained no metal parts and had a more sophisticated triggering device, may have been designed by the same bomb-maker, Ibrahim Hassan al-Asiri, they said. The officials did not say they had captured the bomber or any other individuals, and it was not clear whether anybody had been identified, or whether a suicide bomber had even been recruited yet.
The bomb was seized days before the May 2 anniversary of the death of Osama bin Laden. But the officials said that there was no reason to say it was intended to be used to mark the date, that an attack was never launched and that no plane was ever in danger.
Administration officials continued to say Monday, as they did for days before the anniversary of Bin Laden’s death, which President Obama marked with a trip to Afghanistan and a speech to the nation, that there was no specific threat of a terrorist plot to attack the United States at this time.
A statement Monday from the Department of Homeland Security, however, spelled out the kinds of measures it is taking to prevent being caught off guard, including by this kind of improvised explosive device, or I.E.D.
“Since this I.E.D. demonstrates our adversaries’ interest in targeting the aviation sector, D.H.S. continues, at the direction of the president, to employ a risk-based, layered approach to ensure the security of the traveling public,” Matt Chandler, an agency spokesman, said in a statement. “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.”
The Federal Bureau of Investigation said in a written statement that it possessed the device, which it said had been seized abroad. The bureau is conducting tests on the device, the statement said, and “initial exploitation indicates” that it is very similar to ones used by Al Qaeda in the Arabian Peninsula “in attempted terrorist attacks, including against aircraft and for targeted assassinations.”
Mr. Obama was first told of the plot in April by the White House’s homeland security and counterterrorism adviser, John O. Brennan, and has since received briefings on the matter, according to a statement by the National Security Council.
“While the president was assured that the device did not pose a threat to the public, he directed the Department of Homeland Security and law enforcement and intelligence agencies to take whatever steps necessary to guard against this type of attack,” said Caitlin Hayden, a spokeswoman for the National Security Council. “The disruption of this I.E.D. plot underscores the necessity of remaining vigilant against terrorism here and abroad.”
The plot’s disruption was earlier reported by The Associated Press, which said the government was planning to announce it on Thursday. Other officials confirmed details of the A.P. report.
It was at least the third attempt of the Qaeda affiliate to attack the United States with an aircraft plot using an innovative bomb that officials believe Mr. Asiri designed.
On Christmas in 2009, a young Nigerian tried to blow up an airliner over Detroit with chemical explosives hidden in his underwear, but the explosives merely burned the would-be bomber. Then, in October 2010, Qaeda operatives placed two printer-ink cartridges loaded with explosives and addressed to Chicago aboard cargo planes, but the bombs were detected and removed en route.
Eric Schmitt, Scott Shane and Michael S. Schmidt contributed reporting.