European firms that stop doing business with Iran because of reimposed U.S. sanctions could in turn be sanctioned by the E.U., a special adviser to the 28-country bloc's top diplomat has warned. “If E.U. companies abide by U.S. secondary sanctions they will, in turn, be sanctioned by the E.U.," Nathalie Tocci, an aide to E.U. foreign policy chief Federica Mogherini, told Britain’s BBC Radio 4 on Monday night.