The bomb ripped the roof off the bus packed with students from the nearby University of Haifa, strewing wreckage and body parts onto a main street.
The Haifa blast was the first such attack in Israel since Jan. 5, when a pair of suicide bombers killed 23 people in Tel Aviv.
There was no immediate claim of responsibility for the blast, which comes as Israel’s new hard-line government is pressing ahead with a two-week-old offensive against Hamas militants in Gaza, and as the Palestinian Authority is considering far-reaching reforms.
Responding to Wednesday’s attack, Israel blamed the Palestinian Authority for not preventing suicide bombings. After similar attacks Israel has reacted with tough military measures.
“The Palestinian Authority has been doing absolutely nothing to stop this horrendous blood trail of killing and carnage. There was a deceptive lull in attacks mainly because of the success of our security services,” an Israeli government spokesman said.
Palestinian Cabinet minister Saeb Erekat condemned “any attack that is targeting civilians, whether Palestinian or Israeli.” But he added: “We reject the Israel government finger-pointing that the Palestinian Authority is responsible.”
Abdel Aziz Rantisi, a spokesman for the Islamic militant group Hamas, praised the attack, but did not claim responsibility.
“We will not stop our resistance,” he told the Associated Press. “We are not going to give up in the face of the daily killing [of Palestinians].”
Israeli media reported that the blast was caused by up to 130 pounds of explosives — an exceptionally powerful bomb compared to those used in similar attacks. Its force damaged cars as far as 30 yards away.
Rescue services spokesman Avi Zohar said there were “dozens of casualties, among them at least two dozen seriously injured.”
Ovadia Saar, who was driving another bus just behind the one that was attacked, told the AP that he saw “the back of the bus fly into the air, and the windows blew out and a great cloud of dust covered the bus.”
Police sources said the death toll could rise because there were more body parts at the scene. It was unclear whether the casualty count included the bomber.
Israeli police went on alert throughout the country amid warnings that more attacks were planned, reports said.
The attack comes days after the establishment of a new, right-wing government in Israel. Some of the new government’s key Cabinet ministers have in the past called for Palestinian leader Yasser Arafat’s expulsion.
It also coincides with a two-week-old Israeli military offensive against Hamas strongholds in the Gaza Strip in which dozens of Palestinians have been killed, including some civilians.
Israel stepped up its raids into Gaza after a Feb. 15 attack, in which a bomb blew apart an Israeli tank, killing four soldiers. Hamas claimed responsibility for that bombing.
At least 1,892 Palestinians and 721 Israelis have been killed since this latest intifada, or uprising, began in September 2000.