The U.S.-led military coalition said on Saturday its forces had destroyed a building in the main medical complex of western Mosul that was suspected of housing an ISIS command center.

“The coalition was able to determine through intelligence, surveillance and reconnaissance efforts that ISIS did not use the building for any medical purposes and that civilians were no longer accessing the site,” a coalition statement said.

The terror group disputed the assertion, saying in an online statement that Friday’s strike had killed 18 people, mostly women and children, and wounded 47 others. Independent media have no access to western Mosul or other areas under ISIS control in Iraq and Syria.

The militants are essentially under siege in western Mosul, along with an estimated 650,000 civilians, after U.S.-backed forces surrounding the city dislodged them from the east in the first phase of an offensive that concluded last month.

The coalition said ISIS was using the five-story building as a military command and control facility.

The strike followed reports that the militants are dug in among civilians on the western side of Mosul and storing weapons in hospitals, schools, mosques and churches as a tactic to avoid targeting.

The offensive to dislodge ISIS from Mosul, its last major city stronghold in Iraq, started in October. Iraqi Prime Minister Haider al-Abadi told a meeting of the armed forces commanders on Thursday that the ground offensive on western Mosul could start “very soon”.