But Maj. Curtis J. Kellogg, a spokesman for the U.S. Central Command, said there was "no evidence" of civilian casualties in Hit.
Hit's general hospital received 18 bodies, including three women and eight children, all killed in an airstrike, according to Iraqi news accounts.
"Coalition aircraft attempted to target houses containing ISIS elements, but the [projectiles] fell on the houses of citizens," the report said, using a common acronym for Islamic State.
Hit, a tribal town in the Sunni Muslim stronghold of Anbar, has been under assault since last week by Islamic State forces, which have seized vast stretches of territory in Iraq and neighboring Syria. Many residents have fled the violence.
Hit was also a bastion of anti-U.S. militants during the U.S. occupation that ended in 2011.
Outnumbered Iraqi government forces, which are defending the town, have run out of arms and equipment and were surrounded by Islamic State fighters, according to Iraqi news accounts.
Throughout Iraq and Syria, there have been reports that Islamic State militants have altered their tactics to blunt the effect of U.S.-led airstrikes. The extremists have dispersed positions to present less of a target and moved from exposed bases to areas with considerable civilian populations, observers say.