A bus carrying Israeli youth has exploded in a Bulgarian resort, killing at least seven people and wounding dozens, police and hospital officials said.
Binyamin Netanyahu, the Israeli prime minister, called Wednesday's blast "an Iranian terror attack" and promised a tough response.
The explosion took place in the Black Sea city of Burgas, some 400km east of the capital, Sofia.
Bulgaria's interior minister said on Thursday that the attack might have been carried out by suicide bomber . He said the suspected attacker was carrying a Michigan driver's license that was being sent to the FBI for authentication.
Tsvetan Tsvetanov said the suspected bomber appeared on security camera tape for nearly an hour before the Wednesday attack.
Tsvetanov said the death toll had risen to eight, including the suspected bomber, as the Bulgarian driver of the bus died in the hospital. Six of the victims are Israeli citizens, while the nationality of the suspected bomber remains unknown. Some 30 others were wounded in the attack.
A Hercules jet carrying senior Israeli army officers and trauma surgeons has landed in Bulgaria to help transfer the wounded to the airport for evacuation.
It is expected to land in Tel Aviv on Thursday afternoon, where the wounded will be taken to nearby hospitals.
Images shown on Israeli and Bulgarian media showed smoke billowing from the scene, a parking lot at the local airport, where the Israeli tourists had apparently just landed.
Several buses and cars were on fire near the carcass of the targeted vehicle.
Burgas mayor Dimitar Nikolov, who was at the airport at the time, said the blast ripped through the bus as the tourists who had flown in from Israel were boarding and placing their bags in the luggage compartment, where he suspects the explosives might have been.
"I cannot say if it was an act of terrorism. The blast was very strong and in my view was triggered by a device which was deliberately set," Nikolov said.
Trita Parsi, of the National Iranian-American Counsel, speaking to Al Jazeera from Washington, says so far Tel Aviv has not produced any evidence proving Iranian involvement.
"Only a half hour after the actual incident, Netanyahu went out and accused the Iranians", a time-frame which Parsi says does not leave a lot of time to gather evidence.
"I was on the bus and we had just sat down when after a few seconds we heard a really loud explosion," one Israeli tourist Gal Malka told Israeli army radio. "The whole bus went up in flames."
Aviva, another Israeli woman who was on a nearby bus, said she heard a "very loud explosion" and described seeing at least seven dead bodies.
The bus had on board 47 out of 51 people who had just arrived on a plane from Israel including one American and a Slovenian. The foreign ministry said 154 Israelis arrived on Wednesday at Burgas airport including eight children.
Bulgaria, an eastern European nation bordering Greece and Turkey, is a popular tourist destination for Israelis.
In January, Israeli public television reported that Bulgarian authorities had foiled a bomb attack when they found an explosive device on a bus chartered to take Israeli tourists to a ski resort.
Troops were deployed in several ski resorts frequented by Israeli tourists after the bomb was found, the report said.