SANAA, Yemen — The killings of U.S.-born cleric Anwar al-Awlaki and another American al-Qaida propagandist in a U.S. airstrike have wiped out the decisive factor that made the terrorist group’s Yemen branch the most dangerous threat to the United States: its reach into the West.

Issuing English-language jihad sermons on the Internet from his hideouts in Yemen’s mountains, al-Awlaki drew Muslim recruits like the Nigerian who tried to bring down a U.S. jet on Christmas and the Pakistani-American behind the botched car bombing in New York City’s Times Square.

Friday’s drone attack was believed to be the first instance in which a U.S. citizen was tracked and killed based on secret intelligence and the president’s say-so. Al-Awlaki was placed on the CIA “kill or capture” list by the Obama administration in April 2010 — the first American to be so targeted. A second American, Samir Khan, who edited al-Qaida’s Internet magazine, was also killed in the Friday airstrike.

Late Friday, two U.S. officials said intelligence had indicated that the top al-Qaida bomb-maker in Yemen also died in the strike — Ibrahim al-Asiri, who was linked to the bomb hidden in the underwear of the Nigerian man accused of trying to blow up a plane over Detroit on Christmas Day 2009.

The officials spoke on condition of anonymity because al-Asiri’s death has not officially been confirmed. Al-Asiri is also believed to have built the bombs that al-Qaida slipped into printers and shipped to the U.S. last year in a nearly catastrophic attack.

Christopher Boucek, a scholar who studies Yemen and al-Qaida, said al-Asiri was so important to the organization that his death would “overshadow” the news of the deaths of al-Awlaki and Khan.

Khan published an English-language Web magazine that spouted al-Qaida’s anti-Western ideology and offered how-to articles on terrorism — including “Make a Bomb in the Kitchen of Your Mom.”

The voices of Khan and al-Awlaki made the several hundred al-Qaida fighters hiding in Yemen into a greater threat than similar affiliates of the terror network in North Africa, Somalia or east Asia.

President Barack Obama said the strike is a “major blow to al-Qaida’s most active operational affiliate,” saying the 40-year-old al-Awlaki was the group’s “leader of external operations.”

“In that role, he took the lead in planning and directing efforts to murder innocent Americans,” Obama told reporters in Washington.