Bulgaria began probing Thursday a blast at its Black Sea airport of Burgas that left six people dead and more than 30 injured in the deadliest attack on Israelis abroad since 2004, AFP reports.
Israeli Prime Minister Benjamin Netanyahu immediately blamed arch foe Iran for the explosion that ripped through a bus picking up tourists arriving from Tel Aviv heading for the beaches and seaside resorts of the formerly communist European Union country.
Witnesses described how panicked passengers jumped from bus windows and bodies lay strewn on the ground with their clothes torn off as ambulance sirens wailed and black smoke rose over the airport.
"I was on the bus and we had just sat down when after a few seconds we heard a really loud explosion," one Israeli tourist, Gal Malka, told Israeli army radio. "The whole bus went up in flames."
"Israel will respond forcefully to Iranian terror," Netanyahu said. "In the past few months we have seen attempts by Iran to harm Israelis in Thailand, India, Georgia, Kenya, Cyprus and other places."
US President Barack Obama stopped short of mentioning Iran but slammed what he called a "barbaric terrorist attack" and reaffirmed his "unshakeable commitment to Israel's security."
"My thoughts and prayers are with the families of those killed and injured, and with the people of Israel, Bulgaria, and any other nation whose citizens were harmed in this awful event," he said.
"These attacks against innocent civilians, including children, are completely outrageous. The United States will stand with our allies, and provide whatever assistance is necessary to identify and bring to justice the perpetrators of this attack."
Obama called Netanyahu and expressed his condolences, while both leaders "agreed that Israel and the United States would work together to investigate the attack," said an Israeli government statement.
Netanyahu told Obama that Iran and Hezbollah were waging a global terror campaign, the statement said, and he told the US president that "Iran is a state of global terror. It must bear the consequences of that."
The bombing, which came on the 18th anniversary of an attack on a Jewish community centre in Argentina that killed 85 people, also drew strong condemnation from France and Britain, as well as from Bulgarian Muslim leaders.
Israel also held Iran responsible for the Argentina attack of 1994. The Islamic republic denied the charge and has accused Israel of being behind the assassinations of nuclear scientists and senior military figures in recent years.
Israel's foreign ministry said that Bulgarian Foreign Minister Nikolay Mladenov had told counterpart Avigdor Lieberman by phone that "the explosion was caused by a bomb," while also putting the death toll at seven.
The blast occurred around 1400 GMT on the bus carrying Israelis who had flown in to Burgas, the second largest city on Bulgaria's Black Sea coast, setting off a fire that spread to another two buses, the ministry said.
Israeli media said many on the flight were young Israeli school-leavers who were just about to be drafted into the military.
The Israeli military said it was sending a medical team to Bulgaria "in order to provide medical care and to assist those injured in returning to Israel," a statement said.
Burgas mayor Dimitar Nikolov, who was at the airport at the time, said the blast happened just as the 50 or so tourists were boarding the bus and placing their bags in the luggage compartment.
"I cannot say if it was an act of terrorism. The blast was very strong and in my view was triggered by a device which was deliberately set," Nikolov said.
US Secretary of State Hillary Clinton, who visited Israel on Monday and held talks with Netanyahu on the last stop of a nine-nation tour, said she was deeply saddened and angered to learn of the attack.
"The United States condemns in the strongest terms this heinous terrorist attack against innocent civilians," she said.
Israel and Bulgaria, which has a 13-percent Muslim population, enjoy good relations and the Black Sea coast has become a popular holiday spot for Israelis, with almost 140,000 visiting the country in 2011.
In January, Israeli public television reported that authorities in impoverished Bulgaria had foiled a bomb attack when they found an explosive device on a bus chartered to take Israeli tourists to a ski resort.
Bulgarian troops were deployed in several ski resorts frequented by Israeli tourists after the bomb was found, the report added.