Washington (AFP) - US-led coalition warplanes destroyed a factory in Iraq used by the Islamic State group to make chemical weapons, the Pentagon said Tuesday.

The production center -- a converted pharmaceutical plant complex -- likely made chlorine or mustard gas, said Lieutenant General Jeffrey Harrigian, who heads US Air Forces Central Command.

"This represents just another example of Daesh's blatant disregard for international law and norms," he told Pentagon reporters in a video call, using an Arabic acronym for IS.

The strike occurred Monday near Mosul and was conducted by fighter jets, ground-attack aircraft and even a B-52 heavy bomber, the Pentagon said.

The Pentagon provided video of the strike, showing a series of large, flat-roofed buildings disintegrating under multiple explosions.

Observers have repeatedly alleged IS has used chemical weapons, and the Pentagon has confirmed the jihadists have deployed chlorine and sulfur mustard devices.

Iraqi security forces, backed by coalition air power, are in the final weeks of "shaping" operations ahead of an assault to recapture Mosul, which IS seized in 2014 and which remains the jihadists' last main stronghold in Iraq.