The explosion occurred on Wednesday at Burgas International Airport on the Bulgarian Black Sea Coast, about 400 kilometers (250 miles) east of the Bulgarian capital Sofia, the Israeli daily Haaretz reported.

“There are six bodies on the scene — one critically wounded died at the hospital and two seriously injured are in intensive care. Thirty more people are being treated,” the Israeli Foreign Ministry announced in a statement.

The death toll is expected to rise as more than 40 other people were reportedly on the bus when the incident took place, Bulgarian officials said.

The explosion also damaged two nearby buses.

According to Israeli officials, the explosion took place as the Israeli tourists from a Tel Aviv-Burgas flight were boarding the bus to go to their hotels.

No group has claimed responsibility for the blast so far and the cause of the incident is still under investigation.

“We don’t know if it was a terror attack. We do know it was an explosion,” said Israeli Foreign Ministry spokesman Paul Hirschson.

The southeastern European country is a popular tourist destination for Israelis