Top ISIS Commander 'Omar the Chechen' Believed Dead After Airstrike

— -- The U.S. now believes that senior ISIS military commander Abu Omar al-Shishani, known as Omar the Chechen, has died from injuries sustained in a March 4 airstrike in northeast Syria.

American officials had earlier expressed caution about his status because they did not have concrete proof that he was killed in the attack.

A U.S. official told ABC News today that the U.S. has since determined that al-Shishani, who was originally from the country of Georgia, has died.

Last Friday, Col. Steve Warren, the U.S. military spokesman in Baghdad, told reporters that there had been one survivor from the March 4 airstrike.

Warren explained that there were 13 ISIS members at the location outside the town of al-Shaddadi that was struck by U.S. aircraft. “We know that 12 of them are dead and one of them managed to limp away,” said Warren. The U.S. official said today it has since been determined that the person who initially survived that strike was Omar the Chechen, whose birth name is Tarkhan Tayumurazovich Batirashvili.

A defense official said last Tuesday that the March 4 airstrike was conducted by "multiple waves of manned and unmanned U.S. aircraft." At the time, this official said an initial assessment determined that al-Shishani was "likely killed" in the attack, but urged caution as there was no definitive proof of his death.

The official noted that it was "unusual and noteworthy" that al-Shishani had traveled to the al-Shaddadi area from Raqqa.

"This was likely to bolster the sagging morale of ISIL fighters there, who have suffered a series of defeats by Syrian Democratic Forces as they moved from al-Hawl to al-Shaddadi,” said the official. The town of al-Shaddadi had recently been seized from ISIS by a group of Arab and Kurdish rebels supported by the U.S.

In a statement last Tuesday, Peter Cook, the Pentagon press secretary, characterized al-Shisani as the equivalent of ISIS's "Minister of War."

"He is an ISIL senior commander and Shura Council member based in ar-Raqqah, Syria, and was identified as a military commander in a public video distributed by ISIL. At the time of this strike, [al-Shishani] had been sent to al-Shaddadi to bolster ISIL fighters following a series of strategic defeats to local forces we are supporting, cutting off ISIL operations near the Syria-Iraq border."