Abu Omar al-Shishani was killed "in the town of Sharqat as he took part in repelling the military campaign on the city of Mosul", a website affiliated to Isis stated on Wednesday citing a "military source." However, the statement did not mention when Shishani died. The Pentagon officials have neither confirmed nor denied the report.
The Pentagon said in March that Shishani had likely been killed in a US air strike in Syria, but this was the first time the group appeared to confirm his death.
Shishani's real name was Tarkhan Batirashvili but he was also known as Omar the Chechen. The red-bearded jihadist was said to be a close military adviser to Islamic State leader Abu Bakr al-Baghdadi.
The confirmation came on the Amaq website, which IS regularly uses to issue news and which had denied the Pentagon's claims in March. Amaq said he died trying to repel forces campaigning to retake the city of Mosul.
Last year, the US offered a $5m (£3.5m) reward for Shishani. It said he had held numerous senior military positions within the group, including "minister of war."