The Amaq News Agency, affiliated with ISIS, first posted news of al-Adnani's death in a social media posting on Tuesday.
Later on Tuesday the Pentagon confirmed that an airstrike had targeted al Adnani earlier in the day.
"Today coalition forces conducted a precision strike near Al Bab, Syria, targeting Abu Muhammad Al-Adnani, one of ISIL's most senior leaders," said Peter Cook, the Pentagon Press Secretary, in a statement. ISIL is another acronym used to describe ISIS.
"We are still assessing the results of the strike, but Al-Adnani's removal from the battlefield would mark another significant blow to ISIL" said Cook who described al-Adnani as the "principal architect of ISIL's external operations" in addition to his prominence as the group's top spokesman.
"He has coordinated the movement of ISIL fighters, directly encouraged lone-wolf attacks on civilians and members of the military and actively recruited new ISIL members," said Cook. The U.S. military will continue to prioritize 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."
Al Adnani's stature in the terror organization was so important that only top ISIS leader Abu Bakr al-Baghdadi ranked higher in importance.
Because of his high rank within the ISIS organization, the U.S. Department of State's Rewards for Justice program had placed a $5 million reward for information leading to his death or capture.
In September, 2014 al-Adnani released an audio recording where he called on ISIS sympathizers in the western world. That message has been seen as an inspiration to lone-wolve attacks that have occurred in the United States and France. A U.S.official tied several high-profile ISIS attacks outside of Syria and Iraq to al Adnani's role as the head of external operations.
"Significant operations carried out on his watch include the Paris attacks, the Brussels airport attack, the Istanbul airport attack, the downing of the Russian airliner in the Sinai, the suicide bombings during a rally in Ankara, and the attack on a café in Bangladesh" said the official. "In total, these attacks killed over 1,800 people, and wounded nearly 4,000. Al-Adnani was a legacy AQI member, a Shura council member, and the most publicly recognizable official in ISIL."
"If confirmed, this is a very significant blow for ISIL, and will degrade its ability to direct and inspire terror attacks on the West," said the official.
Rep. Adam Schiff (D-CA), the Ranking Member of the House Permanent Select Committee on Intelligence, released the following statement following reports of al-Adnani's death:
“If the death of Abu al-Adnani is confirmed, it would be a significant blow to ISIS at a time when they are on retreat on the battlefield in Iraq and Syria," said Rep. Adam Schiff (D-Cal), the ranking member of the House Permanent Select Committee on Intelligence in a statement. "Al-Adnani has long been one of the most highly targeted ISIS figures due to his responsibility for external operations, his prominent role as an ISIS spokesman, and his advocacy of lone wolf attacks in the West."
The initial post from Amaq stated that al-Adnani had been killed in Aleppo, but provided no details on how he had died. If al-Adnani died in an airstrike it would also be unclear if he was killed in a targeted strike or of happenstance from an airstrike targeting an ISIS position.
Russian and Syrian regime aircraft conduct airstrikes in the city of Aleppo, but U.S. military aircraft do not fly over the city because U.S. military officials say there is not a large ISIS presence there.
However, American military aircraft conduct airstrikes in eastern Aleppo province that stretches east of the Euphrates River. Recently American airstrikes there have helped with offensives that have retaken the ISIS-held cities of Manbij and Jarabulus.