The airstrike on Oct. 16 was touted as a battlefield success against a key figure loyal to the Islamic State group. American defense officials announced that a recruiter for the militants, Denis Cuspert, a German-born former rapper known as Deso Dogg, had been killed in Syria that day.

But now, the Pentagon says that it was mistaken: Mr. Cuspert had survived the strike near the town of Raqqa.

Maj. Adrian Rankine-Galloway, a Pentagon spokesman, confirmed in an emailed statement on Wednesday: “At the time, our assessment was the strike was successful. It now appears that assessment was incorrect and Denis Cuspert survived the airstrike.”

The major gave no further details, such as when Pentagon officials learned that Mr. Cuspert was still alive. Major Rankine-Galloway said the United States would continue to target terrorists like Mr. Cuspert who work to “plot, conduct or inspire attacks against the West and our allies.”