WASHINGTON (AP) — President Barack Obama declared the killing of a fiery American-born cleric in Yemen a “major blow” to al-Qaida’s most active affiliate, and vowed a vigorous U.S. campaign to prevent the terror network and its partners from finding a haven anywhere in the world.

Anwar al-Awlaki, and a second American, Samir Khan, were killed by a joint CIA-U.S. military air strike on their convoy in Yemen early Friday, U.S. officials said, speaking on condition of anonymity to discuss classified matters. Both men played key roles in inspiring attacks against the U.S., and their killings are a devastating double blow to al-Qaida’s most dangerous franchise.

Seeking to justify the targeted killing of a U.S. citizen, Obama outlined al-Awlaki’s involvement in planning and directing attempts to murder Americans.

“He directed the failed attempt to blow up an airplane on Christmas Day in 2009. He directed the failed attempt to blow up U.S. cargo planes in 2010,” Obama said. “And he repeatedly called on individuals in the United States and around the globe to kill innocent men, women and children to advance a murderous agenda.”

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Yemeni intelligence pinpointed al-Awlaki’s hideout in the town of Al Khasaf, a Yemeni official said, speaking on condition of anonymity to discuss matters of intelligence. “He was closely monitored ever since,” by Yemeni intelligence on the ground, backed by U.S. satellite and drones from the sky, the official said.

After three weeks of tracking the targets, U.S. armed drones and fighter jets shadowed al-Awlaki’s convoy early Friday, then drones launched their lethal strike. The strike killed four operatives in all, officials said, speaking on condition of anonymity to discuss matters of intelligence.

Al-Awlaki was a U.S. citizen, born in New Mexico to Yemeni parents, who had not been charged with any crime. Civil liberties groups have questioned the government’s authority to kill an American without trial.

Al-Awlaki was targeted in the killing, but Khan, who edited a slick Jihadi Internet magazine, apparently was not targeted directly. The identity of the other two al-Qaida suspects is not known, the Yemeni official said.

Khan, who was from North Carolina, wasn’t considered an operational leader but had published seven issues online of Inspire Magazine, a widely read Jihadi site offering advice on how to make bombs and the use of weapons.

Obama praised Yemen’s government and security forces for its close cooperation with the U.S. in fighting Al-Qaida in the Arabian Peninsula, arguably the terror network’s most dangerous affiliate. With al-Awlaki’s death, Obama said the affiliate remains “a dangerous but weakened terrorist organization.”

Following the strike, a U.S. official outlined new details of al-Awlaki’s involvement in anti-U.S. operations, including the attempted Christmas 2009 bombing of a Detroit-bound aircraft. The official said that al-Awlaki specifically directed the man accused of trying to bomb the airliner to detonate an explosive device over U.S. airspace to maximize casualties.

The official also said al-Awlaki had a direct role in supervising and directing a failed attempt to bring down two U.S. cargo aircraft by detonating explosives concealed inside two packages mailed to the U.S. The U.S. also believes al-Awlaki had sought to use poisons, including cyanide and ricin, to attack Westerners.

Al-Awlaki was killed by the CIA working in concert with the same U.S. military unit that got Osama bin Laden — the elite counterterrorism unit known as the Joint Special Operations Command.

Counterterrorism cooperation between the United States and Yemen has improved in recent weeks, allowing better intelligence-gathering on al-Awlaki’s movements, U.S. officials said.

Al-Awlaki is the most prominent al-Qaida figure to be killed since bin Laden’s death in May. But the killing raises questions that the death of other al-Qaida leaders, including bin Laden, did not. Civil liberties groups have questioned the government’s authority to kill an American without trial.

U.S. officials have said they believe al-Awlaki inspired the actions of Army psychiatrist Maj. Nidal Hasan, who is charged with 13 counts of premeditated murder and 32 counts of attempted premeditated murder in the attack at Fort Hood, Texas.

In New York, the Pakistani-American man who pleaded guilty to the May 2010 Times Square car bombing attempt said he was inspired by al-Awlaki after making contact over the Internet.

Al-Awlaki also is believed to have had a hand in mail bombs addressed to Chicago-area synagogues, the air cargo packages intercepted in Dubai and Europe in October 2010.

The senior Democrat on the House intelligence committee, C. A. Dutch Ruppersberger, said that al-Awlaki’s most dangerous operational role was his continual involvement in recruiting Americans willing to carry out terror attacks inside the U.S.

“His whole strategy was to go after individual jihadists inside the U.S. who were willing to go out and attack Americans,” Ruppersberger said, citing the Fort Hood shooting as an example.

Al-Awlaki wrote an article in the latest issue of the terror group’s Internet magazine, justifying attacking civilians in the West. It’s titled “Targeting the Populations of Countries that Are at War with the Muslims.”

Al-Awlaki’s father, Nasser al-Awlaki of Yemen, had sued Obama and other administration officials 13 months ago to try to stop them from targeting his son for death. The father, represented by the American Civil Liberties Union and the Center for Constitutional Rights, argued that international law and the Constitution prevented the administration from assassinating his son unless he presented a specific imminent threat to life or physical safety and there were no other means to stop him.

But U.S. District Judge John Bates threw out the lawsuit in December, saying a judge does not have authority to review the president’s military decisions and that al-Awlaki’s father did not have the legal right to sue on behalf of his son.

Al-Awlaki served as imam at the Dar al-Hijrah mosque in Falls Church, Va., a Washington suburb, for about a year in 2001.

The mosque’s outreach director, Imam Johari Abdul-Malik, has said that mosque members never saw al-Awlaki espousing radical ideology while he was there and that he believes Awlaki’s views changed after he left the U.S.

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Associated Press writers Matt Apuzzo, Julie Pace, Lolita C. Baldor, Adam Goldman, Stephen Braun and Nedra Pickler contributed to this report.

Copyright 2011 The Associated Press.