The U.S.-led coalition fighting the ISterror group says it is investigating reports of an airstrike in a western Mosul neighborhood that allegedly left more than 100 civilians dead.

Residents of the Iraqi city's neighborhood known as Mosul Jidideh told an Associated Press team at the scene that scores of residents are believed to have been killed by a pair of airstrikes that hit a cluster of homes in the area earlier this month.

The coalition says it has "opened a formal civilian casualty credibility assessment on this allegation," according to a statement given to the AP.

Faced with their toughest fight against IS yet, Iraqi and coalition forces have increasingly turned to airstrikes and artillery to clear and hold territory in western Mosul's densely populated neighborhoods.