Islamic State has said that its spokesman and senior commander has been killed while overseeing military operations in northern Syria.
The IS-run Aamaq news agency said Abu Muhammed al-Adnani was "martyred while surveying the operations to repel the military campaigns in Aleppo".
His death, if confirmed, would be the latest blow to the group, which has been on the retreat in Syria and Iraq, where it has declared a self-styled Islamic caliphate straddling both countries.
Al-Adnani, whose real name is Taha Sobhi Falaha, persistently called for attacks against the West, which paid off with the November 13 co-ordinated attacks in Paris that hit a concert hall, a stadium and restaurants and bars, leaving 130 people dead and hundreds wounded.
He is a Syrian who was born in the northern province of Idlib and is believed to be in his late 30s. He crossed the border and joined al-Qaida in Iraq, a precursor to IS, after the 2003 US-led invasion.
In late June 2014, he formally declared the establishment of a caliphate, or Islamic state, stretching across parts of Syria and Iraq, under the leadership of Abu Bakr al-Baghdadi, and demanded allegiance from Muslims worldwide.
A powerful orator, he went on to become the voice of IS. He released numerous, lengthy audio files online in which he delivered fiery sermons urging followers to kill civilians in nations that supported the US-led coalition against the group.
"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 joined a coalition against the Islamic State, then rely upon Allah, and kill him in any manner or way however it may be," al-Adnani said in 2014.
Earlier this year, he called for massive attacks during Ramadan - a call that translated into the bloodiest Muslim holy month in recent memory.
Followers of IS carried out attacks on several continents, including the Orlando shooting in the US, the Nice truck attack in France and a massive suicide bombing in central Baghdad.
Al-Adnani also disparaged Saudi Arabia and its influential clerics for failing to rally behind the rebels that the monarchy supports in Syria like they did decades ago in Afghanistan.
In Washington, Pentagon press secretary Peter Cook confirmed that a US air strike on Tuesday targeted al-Adnani in the Syrian city of al-Bab, which is north-east of Aleppo.
He said: "We are still assessing the results of the strike, but Al-Adnani's removal from the battlefield would mark another significant blow to ISIL (another name for IS).
"Al-Adnani has served as principal architect of ISIL's external operations and as ISIL's chief spokesman. He has co-ordinated the movement of ISIL fighters, directly encouraged lone-wolf attacks on civilians and members of the military and actively recruited new ISIL members.
"The US military will continue to prioritise and relentlessly target ISIL leaders and external plotters in order to defend our homeland, our allies and our partners, while we continue to gather momentum in destroying ISIL's parent tumor in Iraq and Syria and combat its metastases around the world."
Aleppo is a current focal point of the civil war in Syria, where IS, Syrian Kurdish forces, Turkey-backed rebels and President Bashar Assad's forces are vying for control.
The province is frequently struck by US-led coalition airstrikes as well as Russian air raids.
Aamaq vowed revenge against the "filthy cowards in the sect of disbelief". It said a generation raised in IS-held territory would avenge al-Adnani's death.
The Islamic State group has suffered a string of defeats in recent weeks, including in Aleppo province, where Turkish troops and allied Syrian rebels drove IS out of the border town of Jarablus last week.
In Iraq, the group has lost its strongholds in Fallujah and Ramadi, in the western Anbar province. It still controls Mosul, but Iraqi forces are gearing up for a long-awaited operation to retake the country's second largest city.
It has also lost some of its most senior commanders and founding members over the past year, including its "minister of war" Omar al-Shishani, feared Iraqi militant Shaker Wuhayeb, also known as Abu Wahib, and a leading finance official known by several names, including Abu Ali Al-Anbari.