BURGAS, Bulgaria — The attack on a tour bus carrying Israeli vacationers outside the airport here was carried out by a suicide bomber using fake American identification, Bulgarian officials said on Thursday.

Officials in Israel and Bulgaria said that five Israelis had been killed. The Bulgarian driver of the bus was also killed along with the bomber, and dozens more were injured in what Bulgaria, Israel and the United States called a terrorist attack. Israel quickly blamed Iran and promised a firm response. But Nickolay Mladenov, Bulgaria’s foreign minister, said in an interview, “We’re not pointing the finger in any direction until we know what happened and complete our investigation.”

Iranian officials made their first comments on Thursday. The foreign ministry spokesman, Ramin Mehmanparast, said that the Islamic republic, itself the subject of terrorist attacks, condemned the attack in a blanket condemnation of all terrorism.

“Terrorism endangers the lives of innocents,” Mr. Mehmanparast said, according to Iran’s state Arabic-language television channel Al Alam.