SOFIA, Bulgaria >> A lanky, long-haired man wearing a baseball cap and plaid shorts with a fake Michigan driver’s license carried out a deadly suicide attack on a bus full of Israeli vacationers, Bulgarian officials said Thursday.

Israel stuck by its claim that the attack was carried out by Iranian-backed Hezbollah, a Lebanese guerrilla group, and threatened retaliation. Seven people — five Israelis, the Bulgarian driver and the bomber — died in the blast Wednesday.

No group claimed responsibility for the attack. But Israel has attributed a series of attacks on its citizens around the world in recent months to Iran, threatening to escalate a shadow war between the two arch-enemies.

The attack occurred shortly after the Israelis boarded a bus outside the airport in the Black Sea resort town of Burgas, a popular destination for Israeli tourists — particularly for high school graduates before they are drafted into military service — about 400 kilometers (250 miles) east of the capital, Sofia.

Bulgarian television aired security camera footage Thursday showing the suspected bomber wandering in and out of the terminal shortly before the blast. He was dressed as a tourist himself, wearing a baseball cap, T-shirt, plaid shorts and sneakers with short white socks. He carried a large backpack with wheels, as well as a smaller bag.

Interior Minister Tsvetan Tsvetanov said the bomber was believed to have been about 36 years old and had been in the country between four and seven days.

“We cannot exclude the possibility that he had logistical support on Bulgarian territory,” the minister said.

Officials were using DNA samples to try to establish his identity. Bulgarian Prime Minister Boiko Borisov told reporters that a Michigan driver’s license was retrieved, but he said U.S. officials reported that “there was no such person in their database.” Michigan is home to one of the largest Arab communities in the United States.

The Israelis had just arrived on a charter flight from Tel Aviv carrying 154 people, including eight children. Some of them told Israeli television that they were just boarding the white bus in the airport parking lot for a ride to their hotel when the blast occurred.

Officials reported overnight that an eighth person had died, but later said that was incorrect.

Israel’s military said a military plane carrying 33 Israelis injured in the bombing arrived Thursday in Israeli. At least two critically injured Israelis were sent to Sofia for treatment, according to the head of the Israeli military medical corps, Brig. Gen. Itzik Kreis.

A Bulgarian government plane will fly home 100 other Israelis who were not wounded but who want to cut short their vacation.

Bulgarian authorities Thursday dispatched 200 police to hotels where about 1,000 Israelis were staying just north of Burgas. A representative of the Ortanna tour company said about 10,000 Israelis had booked vacations in Bulgaria through the firm this summer and about half had canceled after the attack.

Israel blamed Iran and its Hezbollah proxies for the attack, saying they are waging a campaign against Israeli targets everywhere.

“All signs point to Iran,” Israeli Prime Minister Benjamin Netanyahu said. “This is an Iranian terror attack that is spreading across the world. Israel will react forcefully to Iran’s terror.”

“The direct executors are Hezbollah,” added Israeli Defense Minister Ehud Barak. “Israel will do all it can to find those responsible and punish them, both those who carried it out directly and those who dispatched them.”

Iran’s state TV called Israel’s claims “ridiculous” and “sensational.”

In Berlin, German Foreign Minister Guido Westerwelle urged the Israelis to show restraint until “the real perpetrators and backers” are found.

While Iran denied involvement in Wednesday’s attack, it routinely makes accusations against Israel that feed speculation that it could support attacks on Israeli targets. Iran claims Israel’s Mossad spy agency has been behind the slayings of at least five nuclear scientists since 2010, as well as other clandestine operations such as planting powerful computer viruses.

In April, computer malware known as Flame infiltrated key government networks in Iran and forced a temporary shutdown of Internet links at the Oil Ministry and a key oil shipment facility. In the most recent targeted killing of an Iranian scientist, a director of the country’s main uranium enrichment facility was killed in January when a magnetic bomb attached to his car exploded in Tehran.

Israel has not directly replied to the Iranian charges. But Israeli leaders have repeatedly said that “all options are on the table” in trying to disrupt Iran’s nuclear program — a phrase that is widely interpreted as meaning the possibility of a military strike and other measures that could include cyberwarfare.

In Washington, the Obama administration condemned the blast “in the strongest possible terms.” White House press secretary Jay Carney said U.S. “commitment to Israel’s security remains unshakeable.”

Israel dispatched a military medical and relief team to Bulgaria, a European Union nation of 7.3 million that borders Greece and Turkey.

Bulgaria’s government resisted Nazi demands to deport Jews to death camps in World War II. Many of them migrated to Israel when the Communists seized power after the war. Since the fall of Communism, Bulgaria and Israel have maintained friendly ties.

The Burgas airport was closed and traffic redirected. In Sofia, the capital, Mayor Yordanka Fandakova ordered a stronger police presence at all public places linked to the Jewish community. Some 5,000 Jews live in Bulgaria, most in Sofia.

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Amy Teibel in Jerusalem and Brian Murphy in the United Arab Emirates contributed to this report.