Pentagon officials believe a top bomb-maker for a cell of al-Qaeda jihadists was killed in a U.S. airstrike in Syria earlier this summer, an official said Friday.

The official said it appeared shortly after the July 8 airstrike that David Drugeon, a French-born member of the Khorasan group of al-Qaida operatives, likely was killed, and that officials are now confident that he did not survive the attack. That confidence was bolstered by al-Qaida social media references this week to Drugeon having died, the official said.

The official spoke on condition of anonymity because the U.S. assessment has not been announced.

Officials said in the immediate aftermath of the July airstrike that it killed Muhsin al-Fadhli, a key leader of the Khorasan group, which is a cadre of al-Qaida operatives using Syria as a sanctuary for plotting attacks on the West.

Rep. Adam Schiff, the ranking Democrat on the House Intelligence Committee, said in a statement Friday that if Drugeon's death is confirmed it would be a major setback for al-Qaida in Syria. He reportedly was an expert in building nonmetallic explosives. U.S. officials feared the Khorasan militants would provide these sophisticated explosives to their Western recruits who could sneak them onto U.S.-bound flights.

"One of my greatest concerns is the threat to our nation's airports and airliners, because those kind of attacks have the potential to radically alter our country, damaging an important sector of our economy and further changing the way we live - and those are exactly the type of plots that the Khorasan group has been working on," Schiff said.