As investigation continues to identify suicide bomber behind Bulgaria attack, U.S. officials tell The New York Times that perpetrator was Hezbollah operative under orders from Iran • “This was tit for tat,” in retaliation for assassination of Iranian nuclear scientists, U.S. official says.

The suicide bomber responsible for the bloody attack on a bus carrying Israeli tourists in Burgas on Wednesday was a member of a Hezbollah cell operating in Bulgaria, U.S. officials have told The New York Times.

The information corroborates initial Israeli assertions that the bomber was a Hezbollah terrorist operating under orders from Iran. Prime Minister Benjamin Netanyahu reiterated in a speech Thursday that the attack was perpetrated by "Hezbollah, Iran´s leading terrorist proxy."

A senior U.S. official said told The New York Times that intelligence showed that the bomber, who killed six people and wounded more than 30 in the coastal town of Burgas, had been "acting under broad guidance" to strike Israeli targets abroad, and that this guidance was given to Hezbollah by Iran.

Two other U.S. officials confirmed that Hezbollah was responsible for the attack, but refused to provide additional details.

The official said the bombing was in retaliation for the assassinations of Iranian nuclear scientists, for which Iran has blamed Israeli and Western agents - something that Israel has neither confirmed nor denied. “This was tit for tat,” the U.S. official was quoted as saying.

“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 the bus carrying the Israeli tourists. Iranian President Mahmoud Ahmadinejad apparently alluded to the attack in a speech Thursday, "the Zionist enemy attempts to hit Iran with blow after blow and is hit harder."

A senior source in Jerusalem said on Thursday that last year there were at least 20 attempts to attack Israeli targets abroad. All the attempts were linked to two organizations: Hezbollah or the elite Al- Quds force of the Iranian Revolutionary Guard Corps. The source said that Tehran instructed the two organizations to harm unprotected Israeli civilians abroad and that there is clear information proving the Iranians were involved in the Bulgaria attack.

“They work together when necessary, and separately when not necessary,” the Israeli official told reporters on condition of anonymity.

While the attack is in line with the modus operandi of Hezbollah, the Israeli official said it was unclear whether the attacker intended to detonate himself or he had suffered a "work accident," The New York Times quoted him as saying.

The Bulgarians are still trying to figure out how the bomber entered the country, how he traveled around and where he stayed. There were conflicting reports on Thursday of the bomber´s identity. Bulgarian media initially identified the terrorist as Mehdi Mohammed Ghezali, a Swedish citizen of Algerian decent, and a member of the Global Jihad who had been detained at Guantanamo Bay. Ghezali, 33, was born in Stockholm, to a father of Algerian origin and a mother who hailed from Finland. He grew up in Sweden and was first arrested in 2001 in Pakistan, to where he traveled following the 9/11 terror attacks in New York. Ghezali was reportedly jailed in Guantanamo for a period of time, but was then released following intervention by the Swedish prime minister on his behalf.

Swedish authorities on Thursday denied the reports and denied that Ghezali was the terrorist behind Wednesday´s attack and Bulgarian officials have also denied that he was the bomber.

Israeli and Bulgarian media have repeatedly replayed the images of the suspected terrorist roaming the terminal on Wednesday. Wearing checked Bermuda shorts and blue t-shirt and carrying a small rucksack, the bomber blended in seamlessly with the relaxed crowds travelling to Bulgaria´s sandy Black Sea coast.

The man in his mid-30s, long dark curly hair under dark blue cap, roamed for an hour under the gaze of surveillance cameras through airport buildings and around the car park. Surrounded by Israeli tourists, among tens of thousands who visit Bulgaria every year, it seemed to be just a matter of choosing his target. Some witnesses said when the Israeli tourists boarded the bus, the man ran towards it, pressed himself against the back of the bus and then detonated himself.