Blast on Bulgaria bus carrying Israeli tourists, 4 dead SOFIA (Reuters) - At least four people were killed and dozens injured by an explosion on Wednesday on a bus carrying Israeli tourists outside an airport in Bulgaria that the Israeli prime minister immediately blamed on Iran. The mayor of Burgas, on Bulgaria's Black Sea coast, said the bus was carrying Israeli tourists, but police could not immediately confirm their nationality. Police said several other buses at the site had been damaged. "I do not know what it was, but it was a very powerful blast, and I think it was something placed on purpose in the bus, which carried 47 Israeli tourists," Burgas mayor Dimitar Nikolov told BTV television, adding 33 people were injured. An Israeli witness said in an interview with Israeli army radio that the explosion was probably caused by a suicide bomber at the entrance of the bus. 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 for the Wednesday's blast 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. Israeli officials had previously said that Bulgaria, a popular holiday destination for Israeli tourists, was vulnerable to attack by Islamist militants who could infiltrate via nearby Turkey. Though Tehran has denied involvement, some analysts believe it is trying to avenge the assassinations of several scientists from its controversial nuclear program, which the Iranians have blamed on Israel and its Western allies. Israel has threatened air strikes against Iran's nuclear facilities if diplomatic efforts fail to stop Tehran getting nuclear weapons, which it denies it is seeking. Mayor Nikolov said 171 people had arrived on a plane from Israel to spend their holiday at the Black Sea coast. One American and one Slovenian passenger were on board. The latest information is that four people have died. Three on the scene and one later in hospital. Over 30 people were rushed to hospital," an Interior Ministry spokeswoman said Israeli media said seven people had been killed. Bulgarian police were investigating and could not say at this point what caused the explosion. Burgas airport was closed after the incident and flights were redirected to the airport of Varna, police said. El Al canceled its flight from Tel Aviv to Sofia that was due to leave at 1200 EDT and consequently the turnaround flight. an El Al spokeswoman told Reuters. Nothing has been decided about Thursday's flights. Israeli rescue services were planning to send a plane to Burgas with medical staff to treat the injured and take bodies home, the Israeli ambulance service Magen David Adom said. Writing by Sam Cage; Additional reporting by Ori Lewis in Jerusalem; Editing by Alison Williams