The powerful blast destroyed the bus moments after its driver had rounded a traffic circle in an ultra-Orthodox neighborhood north of downtown, and left in its wake a street stained with blood and littered with bodies, including at least five children.
The attack damaged prospects for a U.S.-backed peace plan that, until yesterday, had helped usher in a period of relative calm. Israeli officials immediately canceled future meetings with Palestinian counterparts and were to convene a security meeting today, raising the possibility of military strikes and a return to the familiar cycle of attacks and counterattacks.
The Palestinian militant groups Islamic Jihad and Hamas made conflicting claims of responsibility for the bombing. Islamic Jihad had vowed to retaliate for the killing last week of one of its senior leaders in the West Bank city of Hebron.
Israeli police said the suicide bombing might have been a joint operation.
Israeli authorities said the bearded bomber may have blended into the crowd of religious passengers by disguising himself as an ultra-Orthodox Jew, wearing a black hat, black coat and white shirt with tassels.
In the ultra-Orthodox neighborhood of Shmuel Hanavi, paramedics worked amid the dead and wounded spilling from the accordion-like midsection of the bus. An infant girl was found alive, trapped under three bodies. The baby did not cry as she was pulled to safety.
"It was a miracle," Yehuda Meshi-Zahav, director of ZAKA, the Hebrew acronym for Identification of Disaster Victims, told reporters as workers behind him stacked white body bags under two small trees in the traffic circle. "I would call this the attack on the children."
Israeli officials said the bombing - in which more than 100 were wounded - was a direct result of the Palestinian Authority's failure to dismantle militant groups, as prescribed in the peace plan known as the "road map," but they stopped short of calling the initiative launched by President Bush two months ago a failure.
"We knew the process was not going to be easy," said Ehud Olmert, a Cabinet minister and former mayor of Jerusalem. "Israel is not ready to give up. Even if there is a slight chance that there are Palestinian elements that are with us to stop terror, we should put it to the test.
"What happened this evening reduces the chances for this," Olmert said. "Either they fight terror or leave us alone and we'll know how to do it without them."
Olmert said he told Palestinian Prime Minister Mahmoud Abbas last month, "If you don't fight terror, you are going to be its victim."
The bomb went off as Abbas was meeting with Islamic Jihad leaders in Gaza in an attempt to persuade them not to retaliate for the killing in Hebron and to preserve a cease-fire he forged seven weeks ago with the three primary armed factions.
"I announce my strong condemnation of this horrible act which does not serve the interest of the Palestinian people at all, and I have given my instructions to the security minister to launch an investigation," Abbas said. "I am really sorry for the families of the victims of this painful incident."
Abbas pleaded with Israel not to respond with military force.
"We will have to wait and be patient and see what will be the reactions," he said. "But I hope that Israel will act wisely, because this would not be in the interest of the peace process."
In Washington, a State Department spokesman reiterated the Bush administration's call for the Palestinian Authority to crack down on militant groups. Before the bombing, Bush had said that he is "happy when there's calm," but stressed that a cease-fire is no substitute for eradicating "organizations that want to kill."
As warnings increased and the peace plan seemed to stall, Israeli officials had warned recently that violence could erupt anew. A relative calm was marred by Israeli army raids in Nablus and Hebron in which Hamas and Islamic Jihad members were killed, followed by twin suicide bombings that killed two Israelis in an Israeli town and in the West Bank.
The Israeli army pulled out of the West Bank city of Bethlehem and repositioned its forces in Gaza as part of a phased withdrawal that was to be coupled with Palestinian moves against militant groups.
Israel had reserved the right to continue targeting wanted Palestinians in areas it controls. But leaders of Palestinian militant groups view such operations as violations of the cease-fire.
"Israel's goal in the coming week will be to break these new rules of the game and to prevent a situation in which every attempted arrest of a wanted man that goes wrong brings the burned buses back to the streets of the major cities," wrote Amos Harzel in a column appearing today in the Israeli newspaper Haaretz.
Israeli leaders have demanded that Palestinian security forces arrest, disarm and dismantle the armed factions, which the Palestinians say they cannot do without triggering a civil war. This week, Israel relented and prepared to withdraw troops from two Palestinian cities, Qalqilya and Jericho, in exchange for a promise by Palestinian officials to contain suspected militants without actually arresting them.
Israeli officials canceled that agreement last night. Israeli newspapers reported that the government indicated that "all political understandings with the Palestinian Authority are void." There was no further explanation.
The bomber yesterday was identified as Rayed Masak, 29, of Hebron, a mosque preacher and father of two. Israeli police said they believe he was from Hamas, and a videotape distributed to news organizations showed him holding an automatic weapon in one hand, a Quran in the other and claiming responsibility on behalf of Hamas.
But Islamic Jihad said in leaflets distributed earlier in Gaza that it had sent the bomber. And a Hamas spokesman in Gaza denied that his organization had carried out the attack.
A Palestinian Authority security official said last night that the confusion could be the result of an internal dispute within the organizations and a split between those based in the West Bank and Gaza Strip.
The bombing was the 100th suicide bombing since the current cycle of violence began in September 2000. The blast occurred about 9:15 p.m. and could be heard more than a mile away, marring a pleasant, cool evening that attracted thousands to downtown restaurants and pubs which have been crowded in recent weeks during the relative calm. Within an hour of the bombing, most of downtown was deserted and businesses closed early.
The bus had left the Western Wall and was jammed with worshipers. Police said they believe the bomber boarded the bus at a stop in Beit Yisrael, a neighborhood adjacent to where it blew up, two blocks from the dividing line with predominantly Arab East Jerusalem.
Witnesses said the bus had just made a turn onto a narrow street when it blew up. A passing tour bus also was damaged by the explosion, its side charred and windows blown out.
"I heard the boom and saw a light so bright it was like the middle of the day," said Mendel Ehrnfeld, 19, a religious student from New York who lives a block from the scene of the bombing. "There were people running from the bus and people running toward it. It was total confusion."
Streets a block away were covered with broken glass, pieces of the bus and human remains - a foot and a bumper shared a sidewalk, tattered clothes lay next to seat cushions and an acrid smell hung in the air. A stream of ambulances rushed away with victims, more than 40 of them children.
Less than a mile away, Israeli Defense Minister Shaul Mofaz had just finished handing out awards to ZAKA, whose leader had decided that because of the cease-fire, yesterday was a safe time to take a break and reorganize. More than 250 of his volunteers were two minutes away when they heard the explosion.
Meshi-Zahev, the group's director, lives in the neighborhood where the bombing occurred and knew many of the victims.
"The hardest part was going body to body and finding my neighbors," he said last night. "I can't imagine how I'm going to face their loved ones."