The bombing of an Israeli tourist bus in Bulgaria was apparently the act of a suicide attacker, the news website novinite.com quoted Prime Minister Boyko Borisov as saying Thursday, dpa reported.
Bulgarian Foreign Minister Nikolay Mladenov told the bTV channel early Thursday that the death toll in Wednesday's blast had risen to eight - seven Israelis and the Bulgarian bus driver.
Of the 37 injured, three in critical condition were flown by a military plane to a hospital in Sofia, 400 kilometres west of Burgas, where the bombing occurred.
Many young people were reported to be among the approximately 40 passengers on the coach when the blast ripped through it at a parking lot of the Burgas airport.
Security cameras filmed a long-haired man in sports attire idling about the location for an hour before the attack, novinite.com said.
His body was found after the explosion. It suffered the worst injuries and the US identification documents he was carrying were believed to be fake, leading authorities to conclude he was the suicide bomber, the website said without citing sources for the information.
Witnesses earlier said the bomb went off after someone boarded one of three buses carrying Israelis, 150 of whom flew in from Tel Aviv around 40 minutes before the attack and were due in a Black Sea resort 30 kilometres away.
Novinite.com said Bulgarian, US and Israeli security services were cooperating in the case.
Israeli leaders accused Iran in the attack and promised a forceful response.