The bombing comes a month after President Trump announced a rapid withdrawal of U.S. forces from Syria BEIRUT—Islamic State claimed responsibility for a bomb blast Wednesday in a Syrian city under U.S.-backed Kurdish control that killed at least three American troops, according to U.S. officials, underscoring the threat the extremist group still poses as the Trump administration prepares to withdraw troops from the country. Local media and the U.K.-based Syrian Observatory for Human Rights reported that allied fighters with the Syrian Democratic Forces and a number of civilians were also among the dead and injured in the attack in the...