The Pentagon Thursday acknowledged targeting a top Islamic State group commander, Omar al-Shishani, in an airstrike, but stopped short of confirming his reported death.

The militant group itself announced Wednesday that Shishani, whose nom de guerre means Omar the Chechen, had been killed.

The Pentagon had already claimed in early March that coalition forces had killed the high-profile rebel leader.

However, Defense Department spokesman Peter Cook said Thursday that the latest strike had been conducted on Sunday and had targeted a leadership meeting near Mosul in Iraq.

"We believe that Omar Shishani was present" with 16 other Islamic State group leaders, he told reporters.

"We believe this was a successful strike but we are not in a position to be able to confirm that he was killed," Cook said.

News of Shishani's death had been carried Wednesday by Amaq, a news service linked to the Islamic State group.

The report did not say when or how he had been killed, simply stating that he died in Shirqat while defending Mosul, the principal city held by the group in Iraq.

Cook acknowledged that American officials had until recently believed Shishani to be dead. But defense officials learned that he was present at the meeting and decided to strike again.

A man in his thirties distinguished by a thick red beard and known as a hardened fighter, Shishani had been in the crosshairs of American officials who portrayed him as an experienced warlord and a kind of minister of defense within the Islamic State group.

The United States had put a $5 million bounty on his head.

Among fellow combatants, he had a reputation as a battle-hardened warrior. A biography produced by an Islamic State group sympathizer and published on the internet described him as an undefeated strategist.

The coalition against the Islamic State has undertaken a campaign to eliminate Islamic State group officials.

President Barack Obama's anti-Islamic State envoy Brett McGurk recently said that the coalition was killing them at a rate of one every three days.