An American service member died from injuries sustained in an improvised explosive device explosion in northern Iraq, the Pentagon said Thursday. The region includes Mosul, the key Iraqi city that has been a stronghold for ISIS fighters since June 2014. An operation was launched earlier this week to liberate Mosul. The troop’s death occurred near Mosul, U.S. defense officials told The Daily Beast. In total, four American troops have been killed in combat since the U.S. re-entered Iraq in 2014, shortly after ISIS took control of Mosul. Earlier this week, Pentagon Press Secretary Peter Cook said American troops would only be serving in advisory roles, and that Iraqi troops would be taking the lead. “Most of the American forces in Iraq are not anywhere close to the front line,” he said.