Bulgarian Prime Minister Boyko Borisov said Thursday that the terror attack at the Sarafovo Airport terminal was likely the work of a suicide bomber, and was not caused by an explosive device planted on the bus, as initially assumed. Seven people were killed, five of them Israelis, and 34 others were wounded in the blast. Related stories: Israeli rescue operation in Burgas underway PM on Bulgaria attack: All signs point to Iran Op-ed: Will Israel respond? Israel and Bulgaria have launched a joint investigation into the terror attack, with collaboration from the FBI and CIA. According to Borisov, Bulgarian security services reviewing airport security footage taken prior to the blast were able to spot a man scouting the area around the buses waiting for the Israeli tourists, for over an hour. According to initial information the man was Caucasian, with long hair, dressed in sports attire. Bulgarian authorities believe he was the suicide bomber since his body was the most torn by the blast, the Sofia-based news agency Novinite reported. The bus (Photo: Reuters) Further information discovered that the suspect's papers included a US passport issued in Michigan, which was apparently a fake. According to the report, an FBI database check failed to match the passport's information with an actual individual. It remains unclear how the man obtained the passport, and how and when he entered Bulgaria, as local authorities have no record of his entering the country. "This heinous attack on the soil of a sovereign state, a member of the European Union, is a provocation meant to sabotage the efforts to promote peace," Borisov said. Bulgarian security services at Sarafovo Airport (Photo: AFP) He added that Bulgaria will do everything in its power to find the perpetrators of the attack and bring them to justice. "I believe the Bulgarian and Israeli peoples will come together to prevent another disaster." He also extended his country's condolences to the families of the victims and wished a speedy recovery to those injured. Bulgaria's Interior Ministry said that security measures in and around hotels where Israeli tourists are staying have been stepped up following the terror attack. Police presence in the district of Burgas has also been beefed up. Meanwhile, an Israeli rescue mission to Burgas is underway: Two IAF C-130 Hercules aircraft landed in Bulgaria Thursday morning, in order to airlift the Israelis injured in Wednesday's terror attack back to Israel. Sarafovo Airport closed immediately after the attack. Elsewhere in Bulgaria, flights headed to Israel were canceled or delayed as well. Follow Ynetnews on Facebook and Twitter Receive Ynetnews updates directly to your desktop