SOFIA, Bulgaria – A bomb exploded on a bus carrying Israeli youth in a Bulgarian resort Wednesday, killing at least six people and wounding 32, officials said. Israeli Prime Minister Benjamin Netanyahu called it “an Iranian terror attack” and promised a tough response.

The explosion took place in the Black Sea city of Burgas, 250 miles east of the capital, Sofia. TV images showed smoke billowing from the scene — a parking lot at the local airport where the Israeli tourists had landed shortly before the blast. Several buses and cars were on fire near the exploded vehicle.

Israeli Foreign Minister Avigdor Lieberman, after being briefed by his Bulgarian counterpart, said the explosion was caused by a bomb placed on the bus. Bulgarian leaders, including the president, rushed to the site, while the Foreign Ministry said authorities were operating under the theory the blast was a terrorist attack.

No group immediately claimed responsibility. But Israelis often have been targeted outside their country, and the attack coincided with the 18th anniversary of the bombing of a Jewish community center in Argentina that killed 85 people.

Israel suspects archrival Iran of being behind several of those assaults. The two nations have long been in dispute over the nature of Iran’s nuclear program. Israel has warned it will use military force to curb Iran’s program if it must because it believes Tehran wants atomic weapons — a charge Iran denies.

The Israeli premier noted that Wednesday’s attack followed similar attacks or attempted attacks in India, Georgia, Thailand and Kenya and Cyprus in recent months. He said that once again, “all signs point to Iran,” though he did not offer any evidence to back up the claim.