Israel accused Iran of orchestrating the bombing of a bus packed with Israeli tourists in a Bulgarian resort town Wednesday that killed at least six people and injured 30 others, adding to tensions across the Middle East.

Fire engulfed the bus and nearby vehicles in an airport parking lot in Burgas, on Bulgaria's Black Sea coast, sending up plumes of dark smoke. Israel's foreign minister, Avigdor Lieberman, said his Bulgarian counterpart told him a bomb was planted on the bus.

Israeli...