WASHINGTON — The Central Intelligence Agency, working closely with foreign partners, thwarted a plot by the branch of Al Qaeda in Yemen to smuggle an experimental bomb aboard an airliner bound for the United States, intelligence officials said on Monday.

The intelligence services detected the scheme as it took shape in mid-April, officials said, and the explosive device was seized in the Middle East outside Yemen about a week ago before it could be deployed.

It appeared that Qaeda leaders had dispatched a suicide bomber from Yemen with instructions to board a flight to the United States with the device under his clothes, but that he had been stopped before reaching an airport. Representative Peter T. King, Republican of New York and chairman of the Homeland Security Committee, said counterterrorism officials had said of the bomber: “We don’t have to worry about him anymore.” He is alive, officials said, but they would not to say whether he was in foreign custody.

But the disclosure was a worrisome sign that Al Qaeda in the Arabian Peninsula remains determined to attack the United States even after a C.I.A. drone strike in Yemen in September killed its two operatives who were American citizens, Anwar al-Awlaki and Samir Khan. American officials said the group had established new training camps after seizing territory in recent months as a result of the upheaval from the Arab Spring.