The suspected suicide bomber in Wednesday’s attack on a tour bus that killed seven and injured dozens was carrying a fake U.S. identification card, the Bulgarian prime minister said.

The suspect, whose nationality has not been determined, had a fake Michigan driver's license, Prime Minister Boiko Borisov said in an interview. Six of the victims on the tour bus are Israeli citizens.

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 -- 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.

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.

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"We cannot exclude the possibility that he had logistical support on Bulgarian territory," the minister said. He declined to elaborate.

Reuters reported that special forces obtained DNA samples for the fingers of the bomber and are attempting to identify him.

"The site is still under investigation," Tsvetanov said. "Our main goal is within the day to gather the necessary evidence."

No group claimed responsibility, but suspicion fell upon Iran and its Lebanese proxy, the Hezbollah guerrilla group. Iran's state TV rejected accusations of Tehran's involvement, saying in a commentary Thursday that claims by Israeli Prime Minister Benjamin Netanyahu and others were "ridiculous" and "sensational."

Israel stood by its stance.

"The direct executors are Hezbollah," Israel Defense Minister Ehud Barak said Thursday. "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."

Israeli Prime Minister Benjamin Netanyahu said that Iran and Hezbollah have been carrying out a "global terror campaign" for more than a year that has targeted Israelis and others.

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.

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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The Associated Press contributed to this report.