This undated image posted on a militant social media account, which has been verified and is consistent with other AP reporting, shows Abu Omar al-Shishani climbing out of a Humvee. (AP Photo via militant social media account)

Abu Omar al-Shishani, one of the Islamic State’s top commanders, has died of wounds suffered from a U.S. airstrike in Syria earlier this month, according to the Pentagon and activist groups in the region.

“We assess he’s dead,” U.S. Army Col. Steve Warren, a spokesman for the U.S.-led coalition in Iraq and Syria, wrote in an email.

Raqqa is Being Slaughtered Silently, a group of activists and citizen journalists reporting from within Islamic State-controlled territory, tweeted confirmation of Shishani’s death Monday night.

According to a release from SITE Intelligence, an organization that monitors extremist groups’ media presence, the Islamic State-linked Amaq News Agency denied Shishani’s death.

Amaq asserted that Shishani “was not exposed to any injury.”

U.S. warplanes and drones targeted Shishani, along with a group of Islamic State fighters outside the Syrian town of Shadadi, in a series of strikes on March 4. Last week, Pentagon officials said they were assessing the outcome of the strikes but could not confirm that he was dead.

Shadadi has been the site of heavy fighting in recent weeks as a rebel alliance called the Syrian Democratic Forces, Syrian Kurds and U.S. advisers have pushed to retake the town — a key intersection near the Iraqi border — from the Islamic State. Pentagon officials said that Shishani’s presence near Shadadi at the time of the airstrikes that ultimately killed him pointed to the significance of the town to Islamic State forces.

Shishani, also known as Omar the Chechen and by his birth name, Tarkhan Tayumurazovich Batirashvili, is a Georgian-Chechen by birth and fought with Chechen militants in 2006 before joining the Georgian army. He served in the army during Georgia’s brief war against the Russians in 2008. By 2012, the red-bearded Shishani had found his way to Syria, where he fought with a number of opposition groups against Syrian President Bashar al-Assad’s forces. Prior to joining the Islamic State, Shishani helped opposition and Islamist forces capture Menagh Air Base from the Syrian army. Last month, the air base was retaken by Kurdish forces.

In 2013, Shishani joined the Islamic State and quickly gained prominence as a capable battlefield commander and strategist. The U.S. Treasury named Shishani as a “specially designated global terrorist” in 2014 and put a $5 million bounty out for any information that could lead to his capture or death.

Shishani has been declared dead numerous times before. In 2014, Russian officials said he had been killed fighting in Chechnya.

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