Israeli Prime Minister Ariel Sharon cut short his U.S. trip to rush back home after meeting with President Bush, who denounced the bombings as ``horrific acts of murder.''
Bush and other world leaders pressed Arafat to crack down on militants. The Palestinian leader ``must do everything in his power to find those who murdered innocent Israelis and bring them to justice,'' Bush said.
Images of bodies lying on sidewalks and blood-smeared survivors crying out in agony filled TV screens, and Israelis had a growing sense that 14 months of Israeli-Palestinian fighting had reached a crossroads. ``It must be understood that we are at a turning point,'' said Cabinet Minister Matan Vilnai. He did not say how Israel would retaliate but warned the Palestinian Authority was ``endangering its existence'' by not cracking down on militants.
The carnage began in Jerusalem just before midnight Saturday, when two suicide bombers set off their nail-filled bombs on Ben Yehuda street, an area of cafes and bars packed with young Israelis. Ten people, mostly teens, were killed, and 150 were wounded.
At noon Sunday, another Palestinian blew himself up in a bus in the northern port city of Haifa, sending bodies flying and destroying the vehicle. Fifteen people were killed and 40 injured.
The Islamic militant group Hamas claimed responsibility for the bombings, in retaliation for Israel's slaying of a Hamas leader nine days ago. Three suicide attackers were killed in the bombings. Hamas said its gunmen were behind the shooting Sunday of an Israeli driver in the Gaza Strip. Israeli soldiers killed the two gunmen in that attack.
Echoing Bush's comments, Russia, Germany, France, Italy, Britain and the European Union demanded Arafat move against groups backing terrorism. Pope John Paul II told pilgrims at the Vatican that the attacks were ``sorrowful and worrisome'' and urged prayers for peace.
Arafat promised to take harsh action against the militants and declared a state of emergency in the Palestinian areas. Palestinian police, accompanied by journalists, began rounding up Islamic militants. An official, speaking on condition of anonymity, said 50 have been arrested and 150 more would be in custody by midnight. Security chief Jibril Rajoub said those involved in the bombings ``would pay the price.''
Skeptical Israelis pointed to a string of past broken promises. ``Arafat will be judged according to his actions, not his declarations,'' said Israeli Foreign Minister Shimon Peres.
In at least six Palestinian refugee camps in Lebanon, gunmen fired in the air to celebrate the bombings. Some Palestinians in the West Bank and Gaza Strip also supported the attacks, with celebratory shots fired outside the home of one of the Haifa bombers.
But some Palestinians said they were tired of the bloodshed. ``The world should help both of us, Israelis and Palestinians, to get out of this pool of blood,'' said Omar Jumma, 31, an engineer in Gaza City.
In a first step, the Israeli military further tightened travel restrictions, barring Palestinians from driving on most West Bank roads. The Defense Ministry said the army would take ``a series of steps'' and that this was ``a critical test'' for the Palestinian Authority.
A U.S. envoy in the region, Anthony Zinni, denounced the attacks as the ``lowest form of inhumanity,'' but said the violence must not derail his efforts to arrange an Israeli-Palestinian truce.
On Sunday, the bomber in Haifa--identified as Maher Habashi, a 21-year-old plumber from the West Bank town of Nablus--got on a crowded city bus, paid his fare, and within seconds detonated the nail-studded explosives belt strapped to his body, witnesses said.
``The bus came down the hill ... and as it leveled out it blew up, it began to run off the road,'' said witness Rachel Antebe.
The blast hurled bodies in the air and blew out the sides off the red-and-white bus.
``I saw the driver of the bus, his face and body covered in blood. I heard people screaming in the bus. I will never forget it,'' said Manal Masri, 32, an Arab resident of the mixed Arab-Jewish neighborhood where the explosion went off.
Thirteen bus passengers and two pedestrians were killed, and about 40 bystanders were wounded, including 10 who were in serious condition, police said.
The attack the night before in Jerusalem came at an hour when the shops, cafes and bars of the Ben Yehuda pedestrian mall were packed with teen-age Israelis.
The two bombers detonated their nail-packed explosives while standing some 40 yards apart. The 10 victims ranged in age from 14 to 20, police said.
``A lot of people were crying, falling, and there was the smell of burning hair,'' said witness Eli Shetreet, 19.
The blasts shattered car windows a block away. Blood was splattered across store fronts, and bits of flesh and metal bolts from the explosives were strewn on the ground. Shortly after the suicide bombings, an explosion went off in a car parked near the mall.
In the West Bank, Palestinian gunmen wounded an Israeli driver near a Jewish settlment and a border guard in two shooting attacks.
Palestinian officials accused Israel of provoking the latest upsurge of violence with its assassination of Mahmoud Abu Hanoud, the leader of the Hamas military wing in the West Bank. Abu Hanoud--who had masterminded several suicide bombings in Israel--was slain on Nov. 23, just days before Zinni arrived for his truce mission.
``The assassination of Abu Hanoud ... provoked the response of the crazy people who did what they did,'' said Rajoub, the Palestinian security chief in the West Bank.
A security official in the Gaza Strip, speaking on condition of anonymity, said Arafat has given orders to carry out mass arrests of Islamic militants and to confiscate illegal weapons. Those speaking out against cease-fire efforts would be muzzled, the official said.
Since the fighting erupted in September 2000, Israel has repeatedly complained that Arafat has done nothing to stop militants who have killed more than 230 Israelis in bombings and shootings. More than 780 people have been killed on the Palestinian side.