Russia claims killing of Islamic State spokesman in Syria
The airstrike hit the Maarat Umm Hawsh area on Tuesday, where some 40 IS militants had been positioned, according to Russia Today.
Reports of the killing were confirmed by the IS-run Aamaq news agency on Tuesday who said Adnani was "martyred while surveying the operations to repel the military campaigns in Aleppo," without providing further details.
His death is a severe blow to the group, which has been on the retreat in Syria and Iraq.
Adnani, who served as the voice of IS over the past few years, is also a senior commander and one of 43 original founders of the terrorist group.
Of the original founders, 41 have been killed so far according to Iraqi terrorism expert Hisham Alhashimi.
Adnani has released numerous, lengthy audio sermons online in which he urged followers to carry out attacks.
Earlier this year, he called for massive attacks during the Muslim holy month of Ramadan.
He is also believed to be the head of the IS group's external operations, and is possibly responsible for recent terror attacks in France, Turkey and elsewhere.
|He swore allegiance to Abu Musab al-Zarqawi, the leader of al-Qaeda in Iraq and rose through the jihadist ranks|
Several terrorism experts have also indicated that Adnani was the presumptive heir to IS leader Abu Bakr al-Baghdadi.
There was no immediate comment or confirmation from Washington of his death.
Aamaq vowed to revenge against the "filthy cowards in the sect of disbelief." It said a generation raised in IS-held territory will take revenge.
Adnani, born Taha Subhi Falaha, was one of the first foreign fighters to cross the border from his native Syria to fight US troops after the 2003 invasion of Iraq.
He swore allegiance to Abu Musab al-Zarqawi, the leader of al-Qaeda in Iraq and rose through the jihadist ranks.
Adnani was reportedly captured in 2005 and imprisoned at a facility run by the US forces, but was freed in 2010.
The Islamic State group has suffered a string of defeats in recent weeks, including in Syria's northern Aleppo province, where Turkish troops and allied Syrian rebels drove IS out of the border town of Jarabulus 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.