Israel accused Iran of carrying out a bomb attack that killed six people on a bus carrying Israeli tourists at a Bulgarian airport Wednesday, and vowed a stern response to Iranian terror.

Photographs and video taken at the airport in the seaside resort of Burgas showed billowing black smoke from the explosion that left the bus a blackened skeleton, scorched several buses nearby, shattered windows and forced the airport to temporarily close, The New York Times reported. Witnesses quoted by Israeli news media said some victims were on fire as they tried to escape the bus. They said many suffered severe burns and that body parts were flung around the parking lot.

We heard a very strong blast. The bus was full with people and children. Flesh and blood everywhere, a Bulgarian witness told TV7 television, Reuters reported. I saw another bus catching fire from the one that exploded. It was complete chaos.

The tourists had arrived on a charter flight from Israel and were on the bus in the car park outside the Burgas airport when the blast ripped through the double-decker. By late evening, the airport was still sealed off and closed as authorities tried to pin down exactly what had happened.

We sat down and within a few seconds we heard a huge boom and we ran away. We managed to escape through a hole on the bus, Aviva Malka told Israeli Army Radio from the scene.

The Bulgarian Interior Ministry declined to comment on whether it might have been a suicide attack, as some witnesses had speculated, and said it was questioning people who had been close to the scene.

The explosion comes on the 18th anniversary of a 1994 bomb attack on the headquarters of Argentina's main Jewish organization by an Iranian-backed Hezbollah suicide bomber, which killed 85 people.

Israeli Prime Minister Benjamin Netanyahu blamed Iran and said Israel would respond.

All the signs lead to Iran. Only in the past few months we have seen Iranian attempts to attack Israelis in Thailand, India, Georgia, Kenya, Cyprus and other places, Netanyahu said in a statement.

Eighteen years exactly after the blast at the Jewish community center in Argentina, murderous Iranian terror continues to hit innocent people. This is an Iranian terror attack that is spreading throughout the entire world. Israel will react powerfully against Iranian terror, he said.

Iran had no immediate comment on Israel's accusations, and no group claimed responsibility for the blast, which the Bulgarian foreign minister said was caused by a bomb placed in the bus's luggage compartment. But if the Israeli accusations are confirmed, the Bulgarian blast would be the first successful attempt by Iranian operatives to kill Israelis in attacks abroad after a string of failed bomb plots targeting Israeli diplomats in Georgia, India and Thailand this year.