The attack, the official said, was in retaliation for the assassinations of Iranian nuclear scientists by Israeli agents, something that Israel has neither confirmed nor denied.
“This was tit for tat,” said the U.S. official, who spoke on condition of anonymity because of the investigation was still under way.
The bombing comes at a time of heightened tensions over Iran’s nuclear program, which Tehran says is for peaceful purposes but Israel and the West say is a cover for developing weapons.
A senior Israeli official said Thursday that the attack in Burgas was part of an intensive wave of terrorist attacks around the world carried out by two different organizations, the Iranian Quds Force, an elite international operations unit within Iran’s Islamic Revolutionary Guards Corps, and Hezbollah.
“They work together when necessary and separately when not necessary,” the official said.
While the Burgas attack fit the modus operandi of Hezbollah, the Israeli official said, it was not clear whether the bomber intended to blow himself up or had suffered what the official called a “work accident,” adding: “We will never know.”
The bomber was carrying a fake Michigan driver’s licence, but there are no indications that he had any connections to the United States, the U.S. official said, adding that there were no details yet about the bomber – his name, age or nationality.
“This looks like he was hanging out for a local target, and when this popped up he jumped on it,” the official said, referring to a tour bus carrying Israeli vacationers outside the airport in Burgas.
Prime Minister Benjamin Netanyahu said at a news conference Thursday in Jerusalem that the attack in Burgas was carried out by “Hezbollah, the long arm of Iran.”
For their part, Iranian officials condemned the attack and all acts of terrorism.
“Terrorism endangers the lives of innocents,” said a spokesman for the Foreign Ministry, Ramin Mehmanparast, according to Iran’s state Arabic-language television channel, Al Alam.
The Bulgarian authorities released a security video Thursday showing the suspect wandering into the arrivals hall at the airport here, for all appearances just another tourist in his plaid shorts, Adidas T-shirt and baseball hat.
But it is his oddly bulky, oversized backpack that, in hindsight, stands out the most. This bag, investigators believe, contained the bomb that the man is suspected of detonating next to a bus outside the airport, killing the five Israeli tourists, a Bulgarian bus driver and himself in a fireball that upended this city on the Black Sea.
The suicide attack, the country’s first, sent police and intelligence officers from Bulgaria, Israel and the United States scrambling to identify the bomber and to look for possible accomplices and convincing evidence that would connect him to Hezbollah or Iran.
Officials here have said they have the man’s fingerprints and his DNA, and are trying to identify a man who was roughly 36 years old, whom they suspect was in the country between four and seven days before the blast.
The Bulgarians are still trying to figure out how the bomber entered the country, how he travelled around the country and where he stayed.