Two American officials confirmed to CNN on Monday that senior Islamic State (ISIS) operative Omar al-Shishani is dead.
The officials said he was injured in a U.S. airstrike last week and then died subsequently, though they would not say how they know he is dead.
On Sunday, the Syrian Observatory for Human Rights said Shishani was “clinically dead” as a result of the airstrike.
However, further assessments have led American officials to conclude he had been injured and later died, according to the CNN report.
He was killed along with 12 additional ISIS fighters in a wave of strikes by drones and manned aircraft.
One reason the U.S. initially thought Shishani had been killed is that intercepts of his communications had gone silent, CNN learned.
The Pentagon has offered different locations for precisely where the strike happened, in one instance saying it was near al-Shaddadi but in a press release indicating it happened near al-Hawl several miles away.
Shishani was one of the ISIS leaders most wanted by Washington which put a $5 million bounty on his head. Also known as Omar "the Chechen" al-Shishani, he was born Tarkhan Tayumurazovich Batirashvili and once served in an elite Georgian military unit.
He reportedly joined ISIS in 2013, a U.S. official said, and later was in charge of a prison near Raqqa, ISIS' “capital” in Syria, where the terror organization might have held foreign hostages.
Shishani instructed the group to transport vehicles and weapons to Syria from Iraq in June 2014, and he was eventually named ISIS' northern commander by leader Abu Bakr al-Baghdadi, overseeing military operations in northern Syria, the defense official told CNN.