Washington: 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 Jan. 24, 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," the statement said.

There have been frequent reports of IS using chlorine gas, but no evidence the group has accumulated a significant chemical weapons cache.

Last year, Iraqi police officers suffered from dizziness and vomiting after clashing with jihadist fighters north of Baghdad. It was thought chlorine gas may have been to blame.

Chlorine gas is classified as a ‘choking agent’, burning the lungs when inhaled in large quantities. But it is nowhere near as dangerous as nerve gases.

Islamic State controls large areas of Syria, where the government has been destroying its chemical weapons, but not all the stockpiles have been accounted for.

The US and its allies has been targeting IS positions in Iraq and Syria since last August, destroying military equipment and killing the group's fighters.

Military chiefs are hoping they can re-take the key city of Mosul with the help of Iraqi forces this spring.

But there are concerns that Iraqi troops are not yet ready to do the fighting needed on the ground.