U.S. military officials say a mid-level Islamic State militant who specialized in chemical weapons was killed in an U.S. air strike near Mosul in Iraq last week.
U.S. Central Command says Abu Malik was killed January 24.
The command said Malik worked at Saddam Hussein's Muthana chemical weapons production facility before joining Al-Qaeda in Iraq in 2005.
Central Command says Malik joined the Islamic State militants, bringing his chemical weapons expertise to the group.
Officials say his death could "temporarily degrade" the group's ability to produce and use chemical weapons.
Coalition air strikes have pounded the Mosul area over the past week.
The U.S.-led coalition has carried out more than 2,000 air raids against IS militants in Syria and Iraq since August 8.
Earlier at a Pentagon briefing, Pentagon spokesperson Rear Admiral John Kirby said that the current operation against IS could last for three to five more years, according to the dpa news agency.
He acknowledged that thousands of air strikes had not brought changes "of great magnitude," adding, "It just shows you, this is going to take a while."
The United States began launching air strikes against Islamic State militants early in August 2014 in a bid to halt its advance in Iraq.
The U.S.-led mission, known as "Operation Inherent Resolve," includes a number of nations.
Some, such as Canada and the United Kingdom, only provide support in Iraq, while others, such as Saudia Arabia and Jordan, carry out air raids in Syria.
As of January 9, the Pentagon estimated that the military campaign had already cost some $1.3 billion.
With reporting by AP and Reuters