Bulgaria said Thursday that a suicide bomber carrying a fake Michigan driver’s license was responsible for an explosion the day before on a bus carrying Israeli tourists, an attack Israel blamed on Iran.

Seven people were killed in the attack, including five Israelis, the Bulgarian bus driver and the bomber, Bulgarian Interior Minister Tsvetan Tsvetanov told reporters in Burgas, the Black Sea city where the bombing took place. Tsvetanov said investigators were using DNA to try to identify the bomber, who video surveillance footage showed had blended into the crowd by wearing shorts and a backpack.

The blast occurred in the late afternoon outside the airport in Burgas shortly after a charter flight carrying 154 people, all but three of them Israeli citizens, arrived from Tel Aviv, the Bulgarian Foreign Ministry said. Israeli and Bulgarian media reported that the travelers had boarded buses that were to take them to a hotel, and the Bulgarian interior minister told Bulgarian radio that explosives had been planted on the vehicle, perhaps in passengers’ luggage. The Foreign Ministry said in a statement that it was “working on the theory that this was a terrorist attack.”

The attack threatened to escalate tensions between Israel and Iran at a time when Israel is proposing military action to prevent Iran from developing nuclear weapons and international efforts to stop the Iranians’ alleged program are faltering.

The blast came five months after Israel blamed Iran for twin bombing attempts targeting Israeli Embassy personnel in India and Georgia, and it fell on the 18th anniversary of a suicide bombing at a Jewish organization in Buenos Aires. That attack, carried out by the Iran-backed Lebanese militia Hezbollah, killed 85 people.

“All signs point towards Iran,” Netanyahu said in a statement. Referring to the Argentina attack, he said: “Deadly Iranian terrorism continues to strike at innocent people. This is a global Iranian terror onslaught and Israel will react firmly to it.”

Israeli Defense Minister Ehud Barak told Israel Radio on Thursday that Hezbollah, an Iran-backed Lebanese militia, was behind the attack, and pledged that Israel would “settle the account.”

“The immediate executors are Hezbollah people, who of course have constant Iranian sponsorship,” Barak said.

Iranian state TV called the Israeli accusations “ridiculous,” the Associated Press reported.

In Washington, President Obama condemned what he called “a barbaric terrorist attack” on Israelis. “As Israel has tragically once more been a target of terrorism,” he said in a statement, “the United States reaffirms our unshakable commitment to Israel’s security, and our deep friendship and solidarity with the Israeli people.”

Israel and Iran are bitter enemies that have been engaged in an escalating rhetorical battle and, security analysts say, a covert war of attacks and assassinations. Israel considers Iran a mortal danger and has threatened to strike its nuclear facilities to prevent it from building a bomb. Although Iran has denied involvement in attacks on Israelis, many analysts believe it has carried out or planned some of them to avenge what it says are Israeli-directed assassinations of some of its nuclear scientists.

Israel had warned recently that Islamist militants might target its citizens in Bulgaria, a popular tourism destination for Israelis. Bulgaria’s Foreign Ministry said 32 people were wounded in Wednesday’s blast, and it was unclear how many of them were Israelis. In a brief statement, the Interior Ministry said that the wounded had been taken to a local hospital and that the airport had been closed.