CIA foiled the plot and took possession of the bomb.
A sophisticated bomb built in Yemen as part of an apparent terrorist plot to destroy Western jetliners is fresh evidence that militants based in Yemen -- not in Afghanistan or Pakistan -- now pose the biggest terror threat to the U.S. and its allies.
U.S. counterterrorism officials said on Monday that the CIA had foiled the plot and taken possession of the bomb, which was described as significantly more powerful than the hidden explosives which another Yemeni-affiliated militant had attempted to detonate aboard a Detroit-bound airliner on Dec. 28, 2009.
The officials stressed that the plot had not advanced to an operational phase and that they were unaware of any current threats to American or European aircraft. They also said they were not sure if the new bomb was a solitary prototype or part of a larger number that had been constructed for potential future use.
Still, the fact that the bomb appears to have been designed and built in Yemen is another indication that the impoverished, politically unstable Middle Eastern country is now the epicenter of transnational terrorism.
In another sign of Yemen's growing centrality to the terror fight, word of the new plot came just a day after a U.S. airstrike killed a militant on the FBI's Most Wanted List for his alleged role in the deadly attack on the USS Cole in 2000.
The Obama administration has reacted to al-Qaida's growing foothold in Yemen by sharply ramping up the number of airstrikes there. The U.S. conducted 10 drone, air, and cruise-missile strikes in all of 2011, according to The Long War Journal, which tracks such strikes. So far this year, it has conducted at least 14, The Journal said.
Those numbers are also set to rise: The CIA recently asked for and received permission to target Yemen-based militants even when American intelligence officials didn't know their names or identities.
With strikes increasing in Yemen, the number of American aerial incursions into Pakistan has begun to decline after years of steady increases. In the first three months of the year, suspected CIA drones launched 11 strikes there, a sizable decrease from the 21 conducted there in the first quarter of 2011, according to data from the New America Foundation.
President Obama's surprise trip to Afghanistan last week was meant to show war-weary Americans that the long conflict there was finally winding down. But the new plot offers a dispiriting reminder that al-Qaida may already have a new home.