An apparently empty bus exploded in Jerusalem on Monday, Haaretz reports, leaving 15 people nearby wounded. Two were in serious condition. The circumstances of the incident remain unclear.

An emergency responder, Mickey Cohen, told Haaretz: “When I arrived at the scene I saw two buses going up in flames and about 10 causalities among them, one who was mortally wounded and another in serious condition. Together with other volunteers from the motorcycle unit of United Hazolah we provided initial medical treatment to the wounded.”

Update – 1:10 pm

According to Reuters, Brachia Sprung, a spokeswoman for Nir Barkat, the Israeli mayor in Jerusalem, said the blast was the result of a detonation. “It was small, but it was definitely a bomb,” she said. Reuters’s bureau chief in Israel and the Palestinian territories, Luke Baker, reported on Twitter, “Israeli police now indicating Jerusalem bus blast caused by an explosive device.”