A top ISIS leader may have been killed during an air strike in the Syrian town of al-Shaddadi, U.S. officials have revealed. Abu Omar al-Shishani has been described by several government officials as the "de facto minister of war" for the terrorist group, the New York Daily News reports. Though no official confirmation has been given from U.S. officials, Shishani is believed to have been killed during the operation. The strike, which took place on Friday, is currently under investigation.

Pentagon officials also estimate that an additional 12 ISIS fighters were killed during the strike, the Washington Post reports. However, as with the fate of Shishani, those numbers remain in flux until final confirmation. Thus far, reports of Shishani’s death have come from anonymous sources within the defense community ahead of an eventual public announcement.

A former member of a Georgian military unit, CNN reports that Abu Omar al-Shishani also had a reward on his head from the U.S. State Department in the amount of $5 million. Abu Bakr al-Baghdadi, the alleged leader of the militant organization, is said to have frequently depended on Shishani's input on the group's day-to-day operations.

After serving time with Georgian forces during the Russian conflict in 2008, Shishani is believed to have spent months in various “rebel brigades” in Syria before ultimately joining ISIS "around 2012 or 2013," according to the Post. Shortly after, Shishani was added to the Treasury Department’s global terrorists list.​