A dozen US warplanes destroyed nearly 50 targets at an "Islamic State" chemical weapons production plant in northern Iraq, the Pentagon said on Tuesday.

The barrage of airstrikes near the terrorist group's stronghold of Mosul targeted a converted pharmaceutical manufacturing plant and headquarters.

Air Force Lt. Gen. Jeffrey Harrigian told reporters the coordinated airstrikes on Monday took out a "significant chemical threat."

IS has been accused of using mustard and chlorine gas against civilian and military targets in both Iraq and Syria.

The airstrikes come as Iraqi security forces conduct "shaping" operations around IS-held Mosul in anticipation of an offensive to retake Iraq's second-largest city.

cw/kl (AFP, AP, dpa)