Mr. Masri was “jihadi royalty, meaning his death will almost certainly necessitate some form of response, whether from Syria or elsewhere in the world,” Mr. Lister said.
The killing of the Qaeda leader was previously reported by CNN and The Guardian. It was confirmed by an American official who declined to be identified because he was discussing classified intelligence reports
Photographs of the vehicle Mr. Masri was said to be traveling in when attacked reveal unusual details for such a strike: The vehicle sustained no major explosive damage, but a projectile clearly struck it directly through the car roof. This suggests the precision strike was either a dud or the United States deliberately used an inert warhead to kill its target by high-velocity impact, avoiding possible civilian casualties with an explosive warhead.
An Egyptian, Mr. Masri real’s name was Abdullah Muhammad Rajab Abd al-Rahman. A veteran of jihadi conflicts in Egypt, Bosnia, Afghanistan and Pakistan, he was a longtime member of Al Qaeda’s highly secretive Shura Council, and was the terrorist group’s key intermediary with its affiliates and other jihadi groups across the world, Mr. Lister said.
His marriage to one of Osama bin Laden’s daughters placed him at the center of Al Qaeda’s hierarchy, and American counterterrorism officials believe he was directly involved in the 1998 bombing of American embassies in East Africa that killed more than 200 people.
After the terrorist attacks on Sept. 11, 2001, Mr. Masri fled to Iran, where he was reportedly put under house arrest along with other senior Qaeda leaders, including Saif al-Adel, the group’s strategic military chief. He was let go by the Iranians in March 2015 along with other Qaeda figures in exchange for an Iranian diplomat who had been kidnapped in Yemen by Al Qaeda in the Arabian Peninsula.
Since then, Mr. Masri had operated in Syria as Al Qaeda’s deputy leader, providing orders and advice to Jabhat Fateh al-Sham, the Qaeda affiliate in Syria formerly known as the Nusra Front, and its leader Abu Mohammed al-Jolani, Mr. Lister said.
Al Qaeda and the Islamic State both operate in Syria. While the Islamic State has its roots in Al Qaeda’s franchise in Iraq, the two terrorist groups split and are now rivals in Syria. The Islamic State has carved out its self-proclaimed caliphate in the eastern part of the country, based in Raqqa. Al Qaeda’s affiliate in Syria is in the northwest and north-central part of the country, centered around Idlib.
The United States and its allies have mostly focused on conducting airstrikes against ISIS in Syria, and on supporting a coalition of Arab and Kurdish fighters on the ground. American airstrikes against Qaeda targets in Syria only increased in the past two months.
In 2005, the United States Treasury Department described Mr. Masri as a Qaeda associate and said that he “was responsible for coordinating Al Qaeda’s work with other terrorist organizations.”
The drone strike against Mr. Masri came about a month after an Air Force B-52 bomber carried out a punishing airstrike against a training camp of Al Qaeda in Syria, which the Pentagon said killed about 100 militants.
That attack, which also included armed drones, was directed at the Shaykh Sulayman Training Camp in Idlib. Pentagon officials said it had been in operation for several years but had only recently become a base for “core Al Qaeda” extremists, who have largely come from outside Syria to fight and plot attacks. All told, 14 bombs and missiles were used in that attack.
The Pentagon disclosed in January that it also carried out an airstrike in Idlib province that killed Mohammad Habib Boussadoun al-Tunisi, described as a Qaeda leader linked to plots against Western targets.
Mr. Boussadoun went to Syria in 2014 after spending several years in Europe and other countries in the Middle East where he maintained ties with extremists, according to a Pentagon statement. Earlier in January, airstrikes killed two other Qaeda leaders, the Pentagon said.