WASHINGTON - (AP) - President Barack Obama declared the killing ofa fiery American-born cleric a "major blow" to al-Qaida's mostactive affiliate, and vowed a vigorous U.S. campaign to prevent theterror network and its partners from finding a haven anywhere inthe world.

Anwar al-Awlaki, and a second American, Samir Khan, were killedby a joint CIA-U.S. military air strike on their convoy in Yemenearly Friday. Both men played key roles in inspiring attacksagainst the U.S., and their killings are a devastating double blowto al-Qaida's most dangerous franchise.

Seeking to justify the targeted killing of a U.S. citizen, Obamaoutlined al-Alwaki's involvement in planning and directing attemptsto murder Americans.

"He directed the failed attempt to blow up an airplane onChristmas Day in 2009. He directed the failed attempt to blow upU.S. cargo planes in 2010," Obama said. "And he repeatedly calledon individuals in the United States and around the globe to killinnocent men, women and children to advance a murderous agenda."

After three weeks of tracking the targets, U.S. armed drones andfighter jets shadowed al-Alwaki's convoy early Friday, then droneslaunched their lethal strike. The strike killed four operatives inall, officials said, speaking on condition of anonymity to discussmatters of intelligence.

Al-Awlaki was targeted in the killing, but Khan, who edited aslick Jihadi Internet magazine, apparently was not targeteddirectly.

Al-Awlaki played a "significant operational role" in plottingand inspiring attacks on the United States, U.S. officials saidFriday. Khan, who was from North Carolina, wasn't considered anoperational leader but had published seven issues online of InspireMagazine, a widely read Jihadi site offering advice on how to makebombs and the use of weapons.

Obama praised Yemen's government and security forces for itsclose cooperation with the U.S. in fighting Al-Qaida in the ArabianPeninsula, arguably the terror network's most dangerous affiliate.With al-Awlaki's death, Obama said AQAP remains "a dangerous butweakened terrorist organization."

Following the strike, a U.S. official outlined new details ofal-Awlaki's involvement in anti-U.S. operations, including theattempted Christmas 2009 bombing of a Detroit.-bound aircraft. Theofficial said that al-Awlaki specifically directed the men accusedof trying to bomb the airliner to detonate an explosive device overU.S. airspace to maximize casualties.

The official also said al-Awlaki had a direct role insupervising and directing a failed attempt to bring down two U.S.cargo aircraft by detonating explosives concealed inside twopackages mailed to the U.S. The U.S. also believes Awlaki hadsought to use poisons, including cyanide and ricin, to attackWesterners.

The U.S. and counterterrorism officials all spoke on thecondition of anonymity in order to discuss intelligence matters. Al-Awlaki was killed by the same U.S. military unit that gotOsama bin Laden. Al-Awlaki is the most prominent al-Qaida figure tobe killed since bin Laden's death in May.

U.S. word of al-Awlaki's death came after the government ofYemen reported that he had been killed Friday about five miles fromthe town of Khashef, some 87 miles from the capital Sanaa.

The air strike was carried out more openly than the covertoperation that sent Navy SEALs into bin Laden's Pakistani compound,U.S. officials said.

Counterterrorism cooperation between the United States and Yemenhas improved in recent weeks, allowing betterintelligence-gathering on al-Awlaki's movements, U.S. officialssaid. The ability to better track him was a key factor in thesuccess of the strike, U.S. officials said, speaking on conditionof anonymity to discuss intelligence matters.

Al-Awlaki's death is the latest in a run of high-profile killsfor the Obama administration. But the killing raises questions thatthe death of other al-Qaida leaders, including bin Laden, did not.

Al-Awlaki was a U.S. citizen, born in New Mexico to Yemeniparents, who had not been charged with any crime. Civil libertiesgroups have questioned the government's authority to kill anAmerican without trial.

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

But U.S. District Judge John Bates threw out the lawsuit inDecember, saying a judge does not have authority to review thepresident's military decisions and that Awlaki's father did nothave the legal right to sue on behalf of his son. But Bates alsoseemed troubled by the facts of the case, which he wrote raisedvital considerations of national security and for military andforeign affairs. For instance, the judge questioned why courts haveauthority to approve surveillance of Americans overseas but nottheir killing and whether the president could order anassassination of a citizen without "any form of judicial processwhatsoever."

U.S. officials have said they believe al-Awlaki inspired theactions of Army psychiatrist Maj. Nidal Hasan, who is charged with13 counts of premeditated murder and 32 counts of attemptedpremeditated murder in the attack at Fort Hood, Texas.

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

Al-Awlaki also is believed to have had a hand in mail bombsaddressed to Chicago-area synagogues, the packages intercepted inDubai and Europe in October 2010.

Al-Awlaki's death "will especially impact the group's abilityto recruit, inspire and raise funds as al-Awlaki's influence andability to connect to a broad demographic of potential supporterswas unprecedented," said terrorist analyst Ben Venzke of theprivate intelligence monitoring firm, the IntelCenter.

But Venzke said the terror group al-Qaida in the ArabianPeninsula will remain the most dangerous regional arm "both in itsregion and for the direct threat it poses to the U.S. followingthree recent failed attacks," with its leader Nasir al-Wahayshistill at large.

Al-Awlaki wrote an article in the latest issue of the terrorgroup's Internet magazine, justifying attacking civilians in theWest. It's titled "Targeting the Populations of Countries that Areat War with the Muslims."

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

The mosque's outreach director, Imam Johari Abdul-Malik, hassaid that mosque members never saw al-Awlaki espousing radicalideology while he was there and that he believes Awlaki's viewschanged after he left the U.S.