"We believe he subsequently died of his injuries," Navy Captain Jeff Davis, a Pentagon spokesman, told AFP.

Officials previously said that Shishani, also known as Omar "the Chechen,"  had been targeted in a March 4 US airstrike near the town of al-Shaddadi in the south of the Hasakah province in northeastern Syria.

Shishani, as one of ISIS most capable commanders, was born Tarkhan Tayumurazovich Batirashvili and has once served in an elite Georgian military unit.

"Batirashvili is a battle-tested leader with experience who had led ISIs fighters in numerous engagements in Iraq and Syria," Pentagon Press Secretary Peter Cook said after the initial strike.

"His potential removal from the battlefield would negatively impact ISIS's ability to recruit foreign fighters — especially those from Chechnya and the Caucus regions — and degrade ISIS's ability to coordinate attacks and defense of its strongholds like Raqqah, Syria, and Mosul, Iraq," Cook added.

According to CNN, he was at a "shura," or meeting with 12 other ISIS terrorists, when the US airstrike hit their venue. He was not killed then, but was injured and later died of his wounds.

He was described as ISIS Iraq and Syria equivalent of a Secretary of Defense and that the US State Department had placed a $5 million reward on his head.

ISIS terrorists, who were initially trained by the CIA in Jordan in 2012 to destabilize the Syrian government, now control large parts of Syria and its eastern neighbor, Iraq.

In September 2014, the US Treasury Department added Shishani along with 10 other militants to the list of Specially Designated Global Terrorists.

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