The officials expressed confidence that the Qaeda leader, Qassim al-Rimi, was killed in a January airstrike in Yemen but were awaiting confirmation before making a public announcement.

If confirmed, his death could represent a significant blow to the Qaeda affiliate, which remains one of the most potent branches of the terrorist group. The Yemen branch, Al Qaeda in the Arabian Peninsula, has tried to attack the United States and Europe and is thought to still want to.

The group’s ability to orchestrate or attack targets in the West has atrophied in recent years, as American airstrikes have targeted their bomb-makers and English-language propagandists. But the group, American officials have previously said, remains a dangerous one.