BAGHDAD—Iraq’s Defense Ministry said Wednesday that an airstrike by the U.S.-led coalition had killed Islamic State’s second-in-command, raising new questions about the group’s leadership.

The militant commander Abu Ala al Afri was one of several people killed in a strike that hit a mosque where Islamic State leaders were meeting, the ministry said. The mosque was in the city of Tel Afar, west of Mosul, the statement said, without disclosing when the strike occurred.

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