JERUSALEM -- An explosion went off Wednesday on a bus killing and injuring an unknown number of people, Israeli police said.
The terror attack was caused by a suicide bomber, Israeli media reported.
Ambulances rushed toward the center of the city on Jaffa Road and victims were taken on stretchers from the blast site.
The bomb comes as the cycle of violence between Israelis and Palestinians threatens to derail the U.S.-backed "road map" to peace.
Hopes for the peace process faltered Tuesday after an Israel a helicopter strike aimed at Hamas leader Abdel Aziz Rantissi, a move which drew criticism from the United States and the Palestinian Authority, and prompted threats of revenge from the militant Islamic group.
Israeli Prime Minister Ariel Sharon was unapologetic Wednesday about the action, telling a Cabinet meeting that "when one talks about terrorism, there are no concessions," according to his office.
Egypt is spearheading attempts to salvage cease-fire negotiations between Palestinian political leaders and militant groups.
Egyptian intelligence chief Omar Suleiman was meeting Wednesday with Palestinian Authority President Yasser Arafat, Palestinian Prime Minister Mahmoud Abbas and Palestinian security chief Mohammed Dahlan. Arafat has been sidelined from peace talks with Israel and the U.S. but remains a key figure among Palestinians.
It is unclear whether Suleiman will travel to Gaza to meet with leaders of Hamas, which the United States and Israel has labeled as a terrorist organization. Hamas said last week it was pulling out of cease-fire talks with the Palestinian Authority, saying Abbas had given up too much at the summit with Sharon and U.S. President George W. Bush in Aqaba, Jordan.
On Tuesday, Israeli missiles struck a jeep carrying Rantissi in Gaza City. Two people were killed in that strike, Palestinian sources said, but Rantissi survived.
From his hospital bed, Rantissi said: "At Hamas, we will not drop our weapons, even if all leaders are assassinated. We will not drop our weapons. This is the only option for the Palestinian people."
Hours later Tuesday, an Israeli Apache struck a car in Gaza that Palestinian militants were using to launch Qassam missiles into Israel, Israeli military sources said. Three Palestinians died in the air attack; at least two of them were bystanders, according to Palestinian sources and witnesses.
President Bush and Abbas both rebuked Israel for the action. Palestinian officials said Sharon is undermining Abbas' efforts to negotiate a cease-fire with militants.
"I am concerned that the attacks will make it more difficult for the Palestinian leadership to fight off terrorist attacks, " Bush said.
Bush added: "I am determined to keep the process on the road to peace. And I believe with responsible leadership by all parties, we can bring peace to the region -- and I emphasize, all parties must behave responsibly to achieve that objective."
Israel defended the operation, saying Rantissi is a key figure in backing terrorist operations and was behind a weekend attack -- a joint operation by militant groups Hamas, Islamic Jihad and Al Aqsa Martyrs Brigades -- that killed four Israeli soldiers in Gaza.
Senior Israeli security sources said Israel gave intelligence information to the Bush administration regarding Rantissi's direct involvement in terror attacks -- some already executed and others in the pipeline -- in an effort to justify the attack.
The road map plan, supported by the United States, European Union, United Nations and Russia, calls for a Palestinian state by 2005, an entity that would live in peace with Israel after a number of steps on both sides.
Among the first steps is a Palestinian effort to end militant attacks on Israeli targets and the Israeli dismantling of "unauthorized outposts" in the West Bank and Gaza.
Abbas and Sharon pledged to carry out those steps at the Aqaba summit, and Israel began dismantling some unoccupied outposts earlier this week.