The Islamic State (ISIS) group’s battle-tested equivalent of a defense minister has “probably” died in an American air strike in Syria, a U.S. official said Tuesday, according to AFP.

The target of the March 4 attack was Omar al-Shishani, a Georgian fighting with ISIS in Syria, the Pentagon said in a statement.

It did not confirm that al-Shishani was killed, saying the result of the attack was still being assessed.

But a U.S. official speaking on condition of anonymity said al-Shishani “likely died” in the assault by waves of warplanes and drones, along with 12 other ISIS fighters.

Omar al-Shishani is one of several ISIS leaders over whom a bounty was placed by the United States last year. He was under a five-million-dollar reward.

The Georgian is accused of overseeing a prison outside the ISIS stronghold of Raqqa where several foreign hostages were held.

His death, if confirmed, would hinder ISIS’s foreign recruitment efforts and its attempts to defend its strongholds in Syria and Iraq, the Pentagon statement said.

Al-Shishani was “the ISIL equivalent of the Secretary of Defense,” the American official said, using an alternative acronym for ISIS.

The U.S. Treasury designated him a foreign terrorist fighter in 2014, and said he maintained “unique authority” within IS.

Batirashvili comes from a town in Georgia that is populated mainly by ethnic Chechens, the official said.

He fought as a Chechen rebel against Russian forces before joining the Georgian military in 2006, and fought Russian forces again in Georgia in 2008.

After being discharged from the Georgian military on health grounds he entered Syria in 2012 and joined ISIS the next year, the official speaking on condition of anonymity said.

The Pentagon statement described Batirashvili as “a battle-tested leader with experience who had led ISIL fighters in numerous engagements in Iraq and Syria.”

AFP contributed to this report.