A senior Islamic State militant whom the United States military tried to kill in an airstrike in Syria last week has died of his wounds, according to a senior Pentagon official.

The militant, Omar al-Shishani, was the Islamic State’s minister of war, according to the Pentagon. The name was an Arab pseudonym for Omar the Chechen, though he was a Georgian national.

The airstrike occurred March 4 near the Syrian city of Shaddadi, where he had gone “to bolster” Islamic State fighters after “a series of strategic defeats to local forces” that are being supported by the United States, the Pentagon said last Tuesday in a statement that announced the airstrike.

At the time, the Pentagon said it was still assessing whether he had been killed. Soon after the strike, jihadists claimed on social media that Mr. Shishani had been wounded, but survived the attack. The senior Pentagon official, speaking on the condition of anonymity to discuss confidential intelligence assessments, said Monday that the United States had confirmed Mr. Shishani’s death, but declined to say precisely when he died or how American spy agencies knew that.