An Islamic State chemical weapons expert was killed in a coalition airstrike last week near Mosul, Iraq, the US Central Command said in a statement on Friday.
Abu Malik, who was killed on 24 January, had been a chemical weapons engineer during the rule of Saddam Hussein and then affiliated himself with al Qaeda Iraq in 2005, Central Command said.
When he joined Islamic State, also known as ISIL, it gave the insurgent force a chemical weapons capability, the statement said. "His death is expected to temporarily degrade and disrupt the terrorist network and diminish ISIL's ability to potentially produce and use chemical weapons against innocent people," it added.
US officials had not publicly referred to Malik previously as a key figure.
There has been no sign that the IS group possesses a major chemical weapons arsenal. But there have been allegations the jihadists have employed chlorine gas, which is classified as a "choking agent", though not as lethal as nerve agents.
Abu Malik, also known as Salih Jasim Mohammed Falah al-Sabawi, had been "involved in operations to produce chemical weapons in 2005, and planned attacks in Mosul with AQI (al Qaeda in Iraq)," said a defence official.
"Based on his training and experience, he was judged to be capable of creating harmful and deadly chemical agents," said the official.
"We know ISIL is attempting to pursue a chemical weapons capability, but we have no definitive confirmation that ISIL currently possess chemical weapons," the official said.
The US-led coalition has carried out more than 2,000 air raids against the IS group in Syria and Iraq since 8 August, including some bombing runs that targeted senior militants.