DUBAI, United Arab Emirates — An Iranian cargo ship believed to be a base for the paramilitary Revolutionary Guard and anchored for years in the Red Sea off Yemen has been attacked, Tehran acknowledged Wednesday. Iran’s Foreign Ministry confirmed the attack — suspected to have been carried out by Israel — on the MV Saviz. The assault came as Iran and world powers sat down in Vienna on Tuesday for the first talks about the U.S. potentially rejoining Tehran’s tattered nuclear deal, showing that the challenges ahead don’t rest merely in those negotiations.