Earlier reports had suggested Omar Shishani, a Georgian whose real name was Tarkhan Batirashvili, may have survived the attack on a convoy.
Several of his bodyguards were killed in the same bombing.
The strike took place on March 4 near the north-eastern town of Shaddadi, where Omar Shishani had reportedly been sent to bolster local ISIS forces.
On March 13, monitoring group the Syrian Observatory for Human Rights said the ISIS leader had been “clinically dead” for several days.
In 2015, the US offered a $5 million reward for Omar Shishani.
It said he had held numerous senior military positions within the group, including “minister of war”.
Last week, the observatory’s director, Rami Abdul Rahman, quoted sources saying that Shishani had been badly wounded and had been taken to a hospital in Raqqa province where he was treated by “a jihadist doctor of European origin”.
US officials have said they believe Omar Shishani was sent to the Shaddadi area to reinforce ISIS militants following a series of military defeats.
Shaddadi was captured last month by the Syrian Arab Coalition, an alliance of Arab rebel groups which joined forces with the Kurdish YPG militia to battle ISIS.
Image source: Wikimedia Commons President-elect Donald Trump celebrated his election victory at the Ultimate Fighting…
Millions of voters across the US chose to return Donald Trump to the White House…
Donald Trump declares victory in the US election as he addresses jubilant supporters in Florida.…
Stocks around the world are rising as Donald Trump appears to be on the cusp…
Donald Trump has won Pennsylvania, North Carolina and Georgia and taken a lead over Kamala…
Quincy Jones, the celebrated musician and producer who worked with Michael Jackson, Frank Sinatra, Ray…