A suicide bomber blew himself up Tuesday on a bus packed with Jewish worshippers returning from the Western Wall, killing at least 18 people, including five children.

Hamas and Islamic Jihad both claimed responsiblity for the blast, one of the deadliest Palestinian attacks in the past three years.

More than 100 people were also injured, 40 of them children, hospital officials said.

The attack marked perhaps the most serious blow yet to the U.S.-backed "road map" peace plan, which was unveiled three months ago. It shattered a truce called by militants on June 29 that had been fraying in recent weeks with less deadly attacks.

In an immediate response, Israel froze all contacts with the Palestinian Authority, as well as the handover of two West Bank towns, Jericho and Qalqiliya, to Palestinian control. The handover had been expected later this week. Israel also decided to seal off the West Bank and Gaza Strip, a security source said.

The powerful explosion ripped through the tandem bus — which has two passenger sections — shortly after 9 p.m. At the time, the bus was heading from the Western Wall, Judaism's holiest shrine, to an ultra-Orthodox Jewish neighborhood on the outskirts of Jerusalem. Many families with children were on the bus, witnesses said.

"I had just come home from praying at the Western Wall and was heading home," said Zvi Weiss, an 18-year-old Jewish seminary student from New York City who sat in the front of the bus and escaped unharmed.

"The bomb went off at the back of the bus. Everything went black. I climbed out of the broken window and started running. All around me there were people covered in blood, screaming, some with limbs missing."

Palestinian Prime Minister Mahmoud Abbas was meeting with Islamic Jihad leaders in the Gaza Strip at the time of the explosion, in a renewed attempt to persuade them to halt attacks.

Abbas condemned the bombing as a "terrible act" and said he ordered Palestinian security forces to investigate. Abbas has been trying to use persuasion, rather than force in handling the militants. It might cost him his job if his approach fails and violence continues.

The road map plan requires the Palestinian security forces to dismantle militant groups, something Abbas has said he cannot do for fear of setting off internal fighting.

In Tuesday's bombing, at least 18 bystanders were killed, including five children, the Zaka rescue service said. Police initially had put the death toll at 20, but there was some confusion because many of the bodies had been dismembered, rescue workers said.

The bus had started out at the Western Wall, Judaism's holiest shrine. One report said among the passengers were members of a family who had celebrated a Bar Mitzvah, the Jewish rite of passage into adulthood for boys, at the Western Wall.

A second bus passing nearby when the explosion went off was also badly damaged, with windows blown out. Rescuers had to use blow torches to get out some of the wounded.

Police said the bomb was very powerful, and had been packed with bits of metal, for greater deadliness.

Shocked survivors, including crying children with blood-smeared faces, were led away from the scene. A paramedic cradled a little girl with a ponytail in his arms, and two others led away an older woman who had blood streaming down her face.

Paramedics treated wounded on the sidewalk, and body parts were strewn on the sidewalk. Later Tuesday, hundreds of people were praying at the site, some holding prayer books. A small group chanted "Death to Arabs!"

In Washington, the White House deplored the bombing and offered sympathies to the victims and their families.

"We condemn this vicious act of terrorism," said Sean McCormack, a spokesman on national security issues. "We call on the Palestinian Authority to dismantle terrorism."

The attack followed a deadly explosion set off by a suicide bomber outside the hotel housing the U.N. headquarters in Baghdad.

An Israeli government spokesman said there was no known direct link between the two bombings, although he said the motivations were similar.

"It is motivated by extremist Islamist militants who don't accept the legitimacy of the West or of Israel," said the spokesman, Dore Gold.

Gold said Israel was paying the price for the Palestinian Authority's inability to rein in militants.

Abbas said he has asked Palestinian security forces to investigate. "I want to declare my full condemnation for this terrible act, which cannot serve the interests of the Palestinian people," he said.

Last week, Islamic Jihad threatened attacks on Israelis to avenge the killing of a senior operative, Mohammed Sidr, in an Israeli arrest raid in the West Bank city of Hebron.

In a phone call to The Associated Press, Islamic Jihad claimed responsibility for Tuesday's bombing, saying it was in revenge for the killing of Sidr, whom Israel had accused of plotting a series of attacks.

However, later Tuesday, Hamas distributed fliers in Hebron, saying the Jerusalem bombing was carried out by one of its supporters, identified as Raed Abdel-Hamed Mesk, 29, a mosque preacher from Hebron.

Hamas released Mesk's farewell video. The plump man with the bushy beard said he was a member of the Hamas military wing, Izzedine al Qassam, accused Israel of violating the cease-fire offered by Hamas.

Mesk's wife Arij began clearing belongings out of her home late Tuesday, in expectation that it would be demolished by Israeli troops. The Israeli military routinely destroys the homes of suicide bombers, hoping it will act as a deterrent.

Arij Mesk said she was not sad. "God gave Raed something he always dreamed of. All of his life he dreamed of being a martyr," she said. The couple has two children, ages two and three.

In the Gaza Strip, a Hamas leader, Abdel Aziz Rantisi, insisted Hamas was not involved."We are committed to the truce. I don't know who carried out this action," said Abdel Aziz Rantisi, a Hamas leader.

(China Daily August 20, 2003)