Senior Islamic State leader, Abu Omar al-Shishani, also known as Omar the Chechen. REUTERS/US. Department of State

The United States has confirmed that top ISIS commander and feared ethnic Chechen jihadi fighter Omar al-Shishani has died of wounds suffered in a U.S. airstrike in Syria, a senior Iraqi intelligence official and the head of a Syrian activist group said Tuesday.

Al-Shishani, whose real name was Tarkhan Batirashvili, was described as ISIS’s equivalent of a Secretary of Defense. He was an ethnic Chechen from the former Soviet Republic of Georgia, specifically from the Pankisi Valley, a center of Georgia’s Chechen community and once a stronghold for militants.

After being wounded in a U.S. airstrike earlier this month, al-Shishani died on Monday outside ISIS’s main stronghold of Raqqa in Syria, according to The Associated Press. A U.S. official previously said an attack was carried out March 4 by multiple waves of planes and drone aircraft.

There was no immediate confirmation of his death from the terrorist group but the ISIS-affiliated Aamaq news agency denied he was killed, saying that the “he was not subjected to any injury.” The outlet quoted an unnamed “source” for the denial, without giving further details or evidence that al-Shishani was still alive.

An American spokesman for the U.S.-led coalition combating the ISIS group in Iraq said the alliance was also confirming the militant commander had died.

The red-bearded militant is one of hundreds of Chechens among the toughest jihadi fighters in Syria. He served as the group’s military commander for the territory it controls in Syria before becoming the commander of the group’s ground forces, according to Hisham al-Hashimi, an Iraqi scholar and author who closely follows the group.

According to Rami Abdurrahman, of the Britain-based Syrian Observatory for Human Rights which tracks the Syrian conflict through a network of activists on the ground, after al-Shishani was wounded, ISIS “brought a number of doctors to treat him, but they were not able to.”

Abdurrahman said al-Shishani died in a hospital in the eastern suburbs of Raqqa. The Iraqi intelligence official, who spoke on condition of anonymity as he was not authorized to talk to the media, said the ISIS commander was buried in Deir el-Zour on Tuesday.

Al-Shishani “had been sent to Shaddadeh to bolster ISIS fighters following a series of strategic defeats,” Pentagon Press Secretary Peter Cook said in the statement.

The spokesman for the U.S.-led coalition, U.S. Army Col. Steve Warren said on Tuesday that the coalition was able to “assess that he is dead” and that it “got the word Monday morning.”

Warren described al-Shishani as a “very important figure,” in the ISIS group, who was hit as part of a stepped-up campaign of U.S.-led airstrikes targeting IS leadership.

Last week, Waren told reporters that the airstrike that targeted al-Shishani was part of a series of stepped-up coalition strikes targeting ISIS leadership.

The extremist ISIS group, which arose from al-Qaida’s branch in Iraq, has many Iraqis among its top leaders. It blitzes across much of Iraq in the summer of 2014, capturing vast swaths of the country’s north and west. It also exploited the chaos of Syria’s civil war to seize large chunks of territory there as well and declared a self-styled “caliphate” on the territory it controls in both countries.

It subsequently drew hundreds of foreign fighters into its operations in Syria. The United Nations estimated that around 30,000 so-called foreign fighters from 100 countries are actively working with the ISIS, al-Qaida or other extremist groups. An earlier estimate by the International Center for the Study of Radicalization, a think tank at King’s College London, said ISIS fighters include 3,300 Western Europeans and 100 or so Americans.

Yet despite the U.S.-led campaign of coalition airstrikes in both Iraq and Syria, ISIS still controls large areas, including Iraq’s second largest city of Mosul and also Raqqa, the group’s main stronghold in Syria.