Responding to one of the deadliest homicide bombings (search) in the past three years, Palestinian Prime Minister Mahmoud Abbas (search) decided Wednesday to cut off contact with Islamic militant groups and will be cracking down on them to prevent further violence.

Abbas condemned Tuesday's homicide attack in Jerusalem (search) that killed 20 and injured more than 100, saying it "cannot serve the interests of the Palestinian people." He ordered Palestinian security forces to investigate.

The Palestinian Authority decided to cut all dialogue with Islamic Jihad (searchand Hamas (search) -- the two groups that claimed responsibility for the bombing -- and instead use security forces to take action against the groups in the coming days, a Palestinian official said on condition of anonymity. It was unclear what sort of action was planned.

The attack Tuesday night was one of the deadliest Israel has seen in the past three years of violence. More than 100 people were injured, 40 of them children, hospital officials said.

• Video: Jerusalem Bus Bombing

The attack marked perhaps the most serious blow yet to the U.S.-backed "road map" (search) peace plan unveiled three months ago.

Israel immediately froze all contacts with the Palestinian Authority and canceled the planned handover of two West Bank towns to Palestinian control, a move that had been expected later this week. The Israeli army also closed border crossings to seal off the West Bank and Gaza Strip.

Early Wednesday, police heightened their patrols throughout Israel.

Abbas was meeting with Islamic Jihad leaders in the Gaza Strip at the time of the explosion, to persuade them to halt attacks.

The homicide bomber, who police said was disguised as an ultra-Orthodox Jew, blew his bomb up in the center of the tandem bus, which has two passenger sections, shortly after 9 p.m. on a main thoroughfare in central Jerusalem.

Many Jewish worshippers had stepped aboard at the Jewish holy site, the Western Wall. The bus was headed to an ultra-Orthodox Jewish neighborhood on the city's outskirts.

"I had just come home from praying at the Western Wall and was heading home," said Zvi Weiss, an 18-year-old 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," Weiss said. "All around me there were people covered in blood, screaming, some with limbs missing."

New York State Assemblyman Ryan Karben, who represents Rockland County, said Goldie Taubenfeld, 43, of New Square, N.Y., was among those killed. He said Taubenfeld's teenage daughter survived and her 6-month-old son is missing. Taubenfeld, a mother of 13, was visiting Israel with her family.

Police said the bomb had been packed with bits of metal for greater deadliness.

The road map plan requires Palestinian security forces to dismantle militant groups, something Abbas has said he cannot do for fear of setting off internal fighting. The militants declared a unilateral truce June 29, but have repeatedly broken their pledge since then.

However, Israeli analysts predicted the sides would continue trying to implement the road map. Alex Fishman, a military correspondent for the Israeli newspaper Yediot Ahronot, said the United States would likely increase its pressure on the Palestinian Authority to round up militants.

"It is absolutely necessary to continue on the political track because the alternative is a return to the never-ending cycle of blood," Fishman wrote.

The bombing drew statements of condemnation and condolences from the United States, the European Union, Britain and the United Nations.

U.N. Secretary-General Kofi Annan urged Abbas "to take decisive action to arrest the instigators of this attack and prevent such attacks from happening again," U.N. spokesman Fred Eckhard said in New York. Annan also urged Israel to "act with restraint in the face of this provocation, and not contribute to a renewed cycle of violence and revenge."

Since the intefadeh began in September 2000, more than 2,400 people have been killed on the Palestinian side and more than 800 on the Israeli side.

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 attacks.

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

Mesk was a close friend of Sidr, Israel Army Radio reported.

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

After the bombing, Israeli troops arrested nine wanted Palestinians in the West Bank, the army said.

The Associated Press contributed to this report.