A top ISIS leader, known as Omar “the Chechen” al-Shishani, was “critically injured” in a U.S. airstrike in northeastern Syria last week, activists for a Syrian opposition group said Wednesday. The U.S. military and intelligence community was assessing Tuesday whether the strike had killed al-Shishani, several U.S. officials told CNN. The strike took place on Friday near the Syrian town of al-Shaddadi. There were also 12 additional ISIS fighters likely killed in the strike, Pentagon spokesman Peter Cook said in a statement. Al-Shishani has a reputation as one of ISIS’ most capable commanders. There has been a $5 million reward on his head from the U.S. State Department. Shishani is a former member of an elite Georgian military unit. “Batirashvili is a battle-tested leader with experience who had led ISIL fighters in numerous engagements in Iraq and Syria,” Cook said in the statement. READ: U.S. claims to have killed 150 fighters from Al-Shabaab in Somalia “His potential removal from the battlefield would negatively impact ISIL’s ability to recruit foreign fighters – especially those from Chechnya and the Caucus regions – and degrade ISIL’s ability to coordinate attacks and defense of its strongholds like Raqqah, Syria, and Mosul, Iraq,” Cook said. Al-Shishani was traveling in convoy in the southern al-Hasakah suburbs when the strike occurred, according to the London-based opposition activist group, Syrian Observatory for Human Rights. He was then transferred to Raqqa, according to the group. Shishani joined ISIS in 2013, the same official said, and later was in charge of a prison near Raqqa 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 said.