U.S. Special Operations forces believe they killed the man some have called ISIS’s “second in command” in an operation inside Syria, according to a senior defense official.

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Haji Imam, whose real name is said to be Abd ar-Rahman Mustafa al-Qaduli, is a senior religious leader of the self-proclaimed Islamic State and had been considered to be next in line to succeed “caliph” Omar al-Baghdadi, though some ISIS watchers say his Turkoman background ruled that out.

The official says U.S. forces killed a high-ranking official in a raid on his vehicle who they believe was Haji Imam, after they tracked him for several days. They had hoped to take him alive, but those in the vehicle apparently resisted and were killed.