(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.

“We have several people killed and dozens of wounded people,” Barak said.

He said 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.

“We are in a continued fight against them. We are determined to identify who sent them, who executed and to settle the account,” Barak said.

Vania Valkova, director of the Bulgarian interior ministry press office, said that at least six people were killed and 30 injured in the explosion outside Burgas Airport on the Black Sea coast.

Bulgaria’s interior minister, who is at the scene, is considering all scenarios, including that of a terror attack, 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.

Netanyahu said his country “would respond with force to Iranian terror.”

Venelin Petkov, a reporter for bTV in Bulgaria, said that three of those taken to the local hospital were in a critical condition.

The Israelis had just arrived from Tel Aviv and were supposed to go to a beach resort about 50 kilometers (31 miles) away, he said.

Israeli Deputy Foreign Minister Danny Ayalon told Israel Radio, “We cannot confirm yet that this is a terrorist incident, but Iran and Hezbollah have been responsible for incidents like this in the past.” Read more