At least seventeen casualties have been reported as a bus exploded in Tel Aviv a block away from the Israeli defence ministry.Israeli police are calling the explosion on Wednesday a "terrorist attack,” and have said that an unidentified package was left in the bus.Emergency services said five of the wounded in the bus explosion were in a serious or moderate condition."We do believe it was a terrorist attack,” Israeli police spokesperson, Mickey Rosenfeld, told Al Jazeera .Israel’s Haaretz newspaper said the blast occurred on the corner of Shaul Hamelech and Henrietta Szold. Most of the injured suffered only mild injuries,” said Ofir Gendelman, a spokesman for Prime Minister Binyamin Netanyahu."The background and circumstances are not clear yet,” police spokeswoman Luba Samri told the AFP news agency.Hamas spokesperson Fawzi Barhoum said that "this is a natural result for the Israeli aggression on our people.”"If the Israel continues its aggression then all options are open.”An Israeli who witnessed the explosion told Army Radio the bus was "completely charred”.Other witnesses reported seeing a man leaving a bomb on the bus and then running off.Al Jazeera’s Tom Ackerman, reporting from Jerusalem, said: "The location of the explosion was a block away from the Israel defence building”.Agencies