SANAA, Yemen (AP) -- In a significant new blow to al-Qaida, U.S. airstrikes in Yemen on Friday killed Anwar al-Awlaki, an American militant cleric who became a prominent figure in the terror network's most dangerous branch, using his fluent English and Internet savvy to draw recruits for attacks in the United States.

The strike was the biggest U.S. success in hitting al-Qaida's leadership since the May killing of Osama bin Laden in Pakistan. But it raises questions that other strikes did not: Al-Awlaki was an American citizen who has not been charged with any crime. Civil liberties groups have questioned the government's authority to kill an American without trial.

The 40-year-old al-Awlaki was for years an influential mouthpiece for al-Qaida's ideology of holy war, and his English-language sermons urging attacks on the United States were widely circulated among militants in the West.

But U.S. officials say he moved into a direct operational role in organizing such attacks as he hid alongside al-Qaida militants in the rugged mountains of Yemen. Most notably, they believe he was involved in recruiting and preparing a young Nigerian who on Christmas Day 2009 tried to blow up a U.S. airliner heading to Detroit, failing only because he botched the detonation of explosives sewn into his underpants.

Yemen's Defense Ministry said another American militant was killed in the same strike alongside al-Awlaki - Samir Khan, a U.S. citizen of Pakistani heritage who produced "Inspire," an English-language al-Qaida Web magazine that spread the word on ways to carry out attacks inside the United States. U.S. officials said they believed Khan was in the convoy carrying al-Awlaki that was struck but that they were still trying to confirm his death. U.S. and Yemeni officials said two other militants were also killed in the strike but did not immediately identify them.

Washington has called al-Qaida in the Arabian Peninsula, as the branch in Yemen is called, the most direct threat to the United States after it plotted that attack and a foiled attempt to mail explosives to synagogues in Chicago.

In July, U.S. Defense Secretary Leon Panetta said al-Awlaki was a priority target alongside Ayman al-Zawahri, bin Laden's successor as the terror network's leader.

The Yemeni-American had been in the U.S. crosshairs since his killing was approved by President Barack Obama in April 2010 - making him the first American placed on the CIA "kill or capture" list. At least twice, airstrikes were called in on locations in Yemen where al-Awlaki was suspected of being, but he wasn't harmed.

Friday's success was the result of counterterrorism cooperation between Yemen and the U.S. that has dramatically increased in recent weeks - ironically, even as Yemen has plunged deeper into turmoil as protesters try to oust President Ali Abdullah Saleh, U.S. officials said.

Apparently trying to cling to power by holding his American allies closer, Saleh has opened the taps in cooperation against al-Qaida. U.S. officials said the Yemenis have also allowed the U.S. to gather more intelligence on al-Awlaki's movements and to fly more armed drone and aircraft missions over its territory than ever before.

The operation that killed al-Awlaki was run by the U.S. military's elite counterterrorism unit, the Joint Special Operations Command - the same unit that got bin Laden.

A U.S. counterterrorism official said American forces targeted a convoy in which al-Awlaki was traveling with a drone and jet attack and believe he's been killed. The official was not authorized to speak publicly and spoke on condition of anonymity.

The Yemeni government announced that al-Awlaki was "targeted and killed" around 9:55 a.m outside the town of Khashef in mountainous Jawf province, 87 miles (140 kilometers) east of the capital Sanaa. It gave no further details.

Local tribal and security officials said al-Awlaki was traveling in a two-car convoy with two other al-Qaida operatives from Jawf to neighboring Marib province when they were hit by an airstrike. They said the other two operatives were also believed dead. They spoke on condition of anonymity because they were not authorized to talk to the press.

Al-Awlaki, born in New Mexico to Yemeni parents, began as a mosque preacher as he conducted his university studies in the United States, and he was not seen by his congregations as radical. While preaching in San Diego, he came to know two of the men who would eventually become suicide-hijackers in the Sept. 11, 2001 attacks on the World Trade Center and the Pentagon. The FBI questioned al-Awlaki at the time but found no cause to detain him.

In 2004, al-Awlaki returned to Yemen, and in the years that followed, his English-language sermons - distributed on the Internet - increasingly turned to denunciations of the United States and calls for jihad, or holy war. The sermons turned up in the possession of a number of militants in the U.S. and Europe arrested for plotting attacks.

Al-Awlaki exchanged up to 20 emails with U.S. Maj. Nidal Malik Hasan, alleged killer of 13 people in the Nov. 5, 2009, rampage at Fort Hood. Hasan initiated the contacts, drawn by al-Awlaki's Internet sermons, and approached him for religious advice.

Al-Awlaki has said he didn't tell Hasan to carry out the shootings, but he later praised Hasan as a "hero" on his Web site for killing American soldiers who would be heading for Afghanistan or Iraq to fight Muslims.

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

After the Fort Hood attack, al-Awlaki moved from Yemen's capital, Sanaa, into the mountains where his Awalik tribe is based and - it appears - grew to build direct ties with al-Qaida in the Arabian Peninsula, if he had not developed them already. The branch is led by a Yemeni militant named Nasser al-Wahishi.

Yemeni officials have said al-Awlaki had contacts with Umar Farouk Abdulmutallab, the accused would-be Christmas plane bomber, who was in Yemen in 2009. They say the believe al-Awlaki met with the 23-year-old Nigerian, along with other al-Qaida leaders, in al-Qaida strongholds in the country in the weeks before the failed bombing.

Al-Awlaki has said Abdulmutallab was his "student" but said he never told him to carry out the airline attack.

The cleric is also believed to have been an important middleman between al-Qaida militants and the multiple tribes that dominate large parts of Yemen, particular in the mountains of Jawf, Marib and Shabwa province where the terror group's fighters are believed to be holed up.

Last month, al-Awlaki was seen attending a funeral of a senior tribal chief in Shabwa, witnesses said, adding that security officials were also among those attending. Other witnesses said al-Awlaki was involved in negotiations with a local tribe in Yemen's Mudiya region, which was preventing al-Qaida fighters from traveling from their strongholds to the southern city of Zinjibar, which was taken over recently by Islamic militants. The witnesses spoke on condition of anonymity for fear of reprisals and their accounts could not be independently confirmed.

Yemen, the Arab world's most impoverished nation, has become a haven for hundreds of al-Qaida militants. The country has also been torn by political turmoil as President Saleh struggles to stay in power in the face of seven months of protests. In recent months, Islamic militants linked to al-Qaida have exploited the chaos to seize control of several cities in Yemen's south, including Zinjibar.

A previous attack against al-Awlaki on May 5, shortly after the May raid that killed Osama bin Laden, was carried out by a combination of U.S. drones and jets.

Top U.S. counterterrorism adviser John Brennan has said cooperation with Yemen has improved since the political unrest there. Brennan said the Yemenis have been more willing to share information about the location of al-Qaida targets, as a way to fight the Yemeni branch challenging them for power.

Yemeni security officials said the U.S. was conducting multiple airstrikes a day in the south since May and that U.S. officials were finally allowed to interrogate al-Qaida suspects, something Saleh had long resisted, and still does so in public. The officials spokes on condition of anonymity to discuss intelligence issues.

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AP correspondent Matt Apuzzo and AP Intelligence Writer Kimberly Dozier in Washington contributed to this report.

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