Mr. Malik was considered a midlevel operative, the official said. He had worked at Saddam Hussein’s Al Muthanna chemical-weapon production facility before he joined the group al Qaeda in Iraq in 2005. As part of al Qaeda in Iraq, Mr. Malik was involved in operations to produce chemical weapons and planned attacks on Mosul with that group, Central Command said.

Al Qaeda in Iraq is the predecessor to the extremist group calling itself Islamic State.

Officials said his knowledge of chemical weapons was a potential threat to civilians in the region. A Central Command spokesman said Islamic State is pursuing chemical-weapons capabilities.

Islamic State militants seized the Al Muthanna facility last June. It contained a stockpile of old weapons, but officials said then that they didn’t believe that the militants would be able to create a functional chemical weapon from the material. The weapons stockpiled there were considered old, contaminated and difficult to move.