Syria’s antiquities chief said Tuesday that the historic city of Palmyra had been unharmed since Islamic State extremists seized it last week. The antiquities official, Maamoun Abdulkarim, said that there was “no damage so far,” but that he was still afraid the group would blow up Palmyra’s 2,000-year-old ruins, which include tombs, a citadel and the Temple of Bel, and which the militants may view as idolatrous. He cited contacts in the central city, which is a Unesco World Heritage site.