Longtime Islamic State spokesman Abu Muhammed al-Adnani was killed in Aleppo, Syria, the Amaq News Agency, the media arm of the terror group, said Tuesday.
He was "martyred while surveying the operations to repel the military campaigns against Aleppo," Amaq said in a statement.
It is unclear whether he was killed by ground forces or in an airstrike, according to the BBC.
Amaq vowed revenge against the “filthy cowards in the sect of disbelief.” It said a generation raised in Islamic State-held territory would seek revenge.
Adnani, 39, had appeared in Islamic State media since 2011 and was one of its primary leaders to call for "lone wolf" attacks, the SITE Intelligence Group reported.
Adnani, a founding member of the Islamic State, oversaw a recruiting and training operation that led to attacks on Europe, according to multiple media outlets. He called for attacks this year in Western countries, telling Muslims in France to attack “the filthy French” in any way they could, including “crush them with your car,” the Associated Press reported.
If his death is confirmed by the United States or other nations, it would be the latest blow to the terrorist group.
The Islamic State, also known as ISIL or ISIS, took control of a large swath of Iraq and Syria in 2014, but it lost some ground in recent months. The group's battlefield struggles come as lone wolf attacks have flourished, including those in San Bernardino, Calif., and in Orlando.
The U.S. State Department designated Adnani a Specially Designated Global Terrorist on Aug. 18, 2014.