SOFIA, Bulgaria (AP) — A bomb exploded on a bus carrying Israeli youth in a Bulgarian resort yesterday, 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, some 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 shell of 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. He said seven people died, but by last night the Bulgarian Foreign Ministry had placed the death toll at six and the number of wounded at 32. 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 yesterday's attack coincided with the 18th anniversary of the bombing of a Jewish community centre 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 programme. Israel has warned it will use military force to curb Iran's programme if it must because it believes Tehran wants atomic weapons -- a charge Iranian officials deny.

The Israeli premier noted that yesterday'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.

"This is an Iranian terror attack that is spreading across the world," Netanyahu said. "Israel will react strongly to Iran's terror."

The US, which has preferred to pursue sanctions and diplomatic pressure against Iran in the nuclear dispute, also strongly condemned what President Barack Obama called a "barbaric terrorist attack". British Foreign Secretary William Hague also called it terrorism and expressed condolences to the families of the victims.

Tehran did not immediately issue any comment.

Bulgaria, a majority Orthodox Christian country of 7.3 million that borders Greece and Turkey, is a favourite tourist destination for Israelis. In recent years, Burgas has become popular as an inexpensive haven for groups of Israeli teenagers taking trips after finishing high school and before their military service.

Lieberman said the bus was transporting tourists who had arrived in a charter flight from Israel. There were 154 people on the flight.