Islamic State's official spokesman, Abu Muhammad al Adnani, has reportedly been killed near Aleppo.
Quoting a "military source," the Islamist group's Amaq News Agency reported he was killed "while surveying the operations to repel the military campaigns against Aleppo".
A US defence official said it carried out an airstrike in Al Bab, Syria, targeting a senior Islamic State official, but he stopped short of confirming al Adnani was the target.
The jihadi was identified by the US in 2014 as a Specially Designated Global Terrorist and senior leader for IS and a reward of up to $5m was offered for information that would lead to him.
The militant had been one of the last remaining members alive of the original group that founded IS, along with the group's self-appointed caliph Abu Bakr al Baghdadi.
As head of external operations, he was in charge of attacks overseas, an increasingly important tactic for the group as its core Iraqi and Syrian territory has been eroded by military losses.
The US State Department declared him to be: "The main conduit for the dissemination of IS messages, including its declaration of IS' creation of an Islamic caliphate."
A Syrian originally from Aleppo, al Adnani pledged allegiance to Islamic State's predecessor al Qaeda more than a decade ago and according to the Brookings Institute he was once imprisoned by US forces in Iraq.
In 2014 he issued a statement calling for the killing of non-Muslim citizens of coalition governments engaged in the fight against Islamic State.
"If you can kill a disbelieving American or European - especially the spiteful and filthy French - or an Australian, or a Canadian, or any other disbeliever from the disbelievers waging war, including the citizens of the countries that entered into a coalition against the Islamic State, then rely upon Allah, and kill him in any manner or way however it may be," he said.
In May 2016 he issued a statement calling for the execution of so-called lone-wolf attacks in countries preventing jihadis from travelling to Iraq and Syria to fight alongside the Islamic State.
"If the (governments) have shut the door of hijra (emigration to the caliphate) in your faces, then open the door of jihad in theirs," he said.
Al Adnani, whose birth name is Taha Sobhi Falaha, was reportedly wounded during an airstrike in the Iraqi town of Barwanah in January before he moved to Mosul, Islamic State's de facto capital in Iraq.
