A high-ranking Yemeni security official, speaking on condition of anonymity, said that Mr. Awlaki was killed while traveling between Marib and Jawf Provinces in northern Yemen — areas known for having a Qaeda presence and where there is very little central government control.

A tribal sheik from Jawf Province, Abdullah al-Jumaili, said he had seen the place where Mr. Awlaki was killed. Reached by phone in Jawf, Mr. Jumaili said that the car Mr. Awlaki and two or three companions had been traveling in was nearly destroyed, and that it might be difficult to recognize bodies. But he said he had also spoken to other tribesmen in the area and was “100 percent sure” that Mr. Awlaki had been killed.

There had been an intense debate among lawyers in the months before the Obama administration decided to put Mr. Awlaki on a target list in early 2010, and officials said that Mr. Khan was never on the list. The decision to make Mr. Awlaki a priority to be sought and killed was controversial, given his American citizenship. The American Civil Liberties Union, which fought unsuccessfully in the American court system to challenge the decision to target Mr. Awlaki, condemned the killing.

Mr. Awlaki’s death comes in the midst of a deepening political crisis in Yemen, the Arab world’s poorest country, where President Ali Abdullah Saleh has been resisting repeated calls to relinquish power. Mr. Saleh has argued that he is essential to the American efforts to battle Al Qaeda in Yemen, but American officials said there was no connection between Mr. Saleh’s abrupt return this week from Saudi Arabia, where he had been recovering from injuries sustained in an assassination attempt, and the timing of Friday’s airstrikes.

Born in New Mexico to Yemeni parents, Mr. Awlaki, 40, began preaching in mosques while a college student in the United States. During that time, as a preacher in San Diego, he met two of the Sept. 11, 2001, attackers. He returned to Yemen in 2004 and his English-language sermons became ever more stridently anti-American.

American counterterrorism officials said his Internet lectures and sermons inspired would-be militants and led to more than a dozen terrorist investigations in the United States, Britain and Canada. Maj. Nidal Malik Hasan, who is accused of killing 13 people in a shooting rampage at Fort Hood in Texas in 2009, had exchanged e-mails with Mr. Awlaki before the shootings. Faisal Shahzad, a Pakistani-American who tried to set off a car bomb in Times Square in May 2010, cited Mr. Awlaki as an inspiration.