CNN) -- A deadly explosion on a bus carrying Israeli tourists at an airport in Bulgaria is "clearly a terrorist attack," Israeli Defense Minister Ehud Barak said Wednesday.
Key Israeli politicians pointed to Iran as the likely instigator.
Vania Valkova, director of the Bulgarian Interior Ministry press office, said that at least six people were killed and about 30 injured in the explosion in a parking lot outside Burgas Airport, on the Black Sea coast. The Foreign Ministry said six died and 32 people were injured, with three in intensive care.
The attack was probably initiated by a group under the auspices of "either Iran or other radical Muslim groups" and named Hezbollah and Hamas as likely suspects, according to Barak. "We are in a continued fight against them. We are determined to identify who sent them, who executed (the attack) and to settle the account," Barak said.
Bulgaria's interior minister, who is at the scene, is considering all scenarios, including that of a terrorist attack, Valkova said.
The country's foreign minister, Nikolai Mladenov, said, "We're assuming all possibilities, including an act of terrorism." Bulgaria will ask the U.N. Security Council to condemn the bombing Thursday, Mladenov said.
The bus was supposed to carry about 47 passengers to a resort.
Another spokeswoman for the interior ministry said one possibility is that an explosive device could have been on the bus, but authorities cannot be sure of it. A forensic team has begun an investigation at the scene, but much work remains to be done, she said.
Israeli Prime Minister Benjamin Netanyahu pointed the finger at Iran, saying it has been behind a string of recent attempted attacks on Israelis in Thailand, India and Georgia, among others.
"All the signs (are) leading to Iran," he said, according to a statement from his office. "This is a global Iranian terror onslaught and Israel will react firmly to it."
Netanyahu said his country "would respond with force to Iranian terror." Bulgarian authorities also vowed to find out what happened.
Israel's intelligence minister told CNN's Christiane Amanpour that Israel has "very good indications" Iran was involved.
"They are after us, Israelis, wherever they can find them," said Dan Meridor. "It's an atrocity attack, against civilians. It needs to be stopped. We need to find out who did it and react promptly as we should."