US-led coalition airstrikes continued to hit ISIS positions in northern Iraq, as ground forces move closer to the terror group's main Iraqi stronghold in Mosul, the largest city the group still controls in the country.

On September 15, the coalition hit what it called an improvised explosive device factory near Mosul, as the GIF below shows.

The September 15 strike came just three days after airstrikes on what Operation Inherent Resolve officials called an ISIS headquarters facility that was used to produce chemical weapons.

"Intelligence indicated that Da’esh converted a pharmaceutical plant complex into a chemical weapons production capability, using chlorine or mustard gas," the US Air Force Central Command official told Business Insider at the time, referring to ISIS by another name. "This represents another example of Da’esh’s blatant disregard for international law and norms."

A displaced man from south of Mosul gives the coordinates of Islamic State militants to Iraqi soldiers south of Mosul. Thomson Reuters

In the latter half of September, the US-led anti-ISIS coalition conducted dozens of airstrikes in Iraq and Syria, targeting fighting positions and tactical units, as well as destroying buildings, vehicles, weapons-production facilities, and other infrastructure.

The strikes come as Iraqi forces and allies on the ground in northern Iraq advance on Mosul.

In late September, US Defense Secretary Ash Carter announced a deal that would send 615 additional US troops to aid Iraqi efforts to retake the city, bringing the US presence in Iraq to 5,262 troops.

The US and others have also stepped up aid supplies to Iraq in anticipation of population displacement and other hardships arising from the advance on Mosul.

See the full video of the September 15 airstrike on the Operation Inherent Resolve Facebook page.