Associated Press

Medics carry the body of an unidentified victim as Israeli police and investigators search the wreckage of a bus after it was bombed in the northern Israeli port city of Haifa yesterday. A suicide bomber detonated nail-studded explosives on a bus in Haifa, killing himself and 15 bystanders just hours after Islamic militants set off three deadly explosions in downtown Jerusalem.

HAIFA, Israel - A Palestinian suicide bomber detonated nail-studded explosives on a bus full of Israelis in this port city yesterday, killing 15 people, just hours after Islamic militants set off deadly explosions in downtown Jerusalem.

The two suicide attacks and a Gaza shooting killed 26 people - many of them teens - and injured nearly 200. Under pressure at home to respond harshly, Prime Minister Ariel Sharon decided to cut short his trip to the United States. He moved a meeting with President Bush up to yesterday so he can return to Israel the same day.

The Palestinian militant group Hamas, which had vowed to avenge Israel's slaying of one of its leaders last month, claimed responsibility for the attacks. The deadliest wave in 14 months of Israeli-Palestinian fighting came as a U.S. envoy was trying to arrange a truce.

Bush called the suicide attacks "horrific acts of murder" and said terror must not be allowed to "destroy the chance of peace."

He called on Palestinian leader Yasser Arafat to track down those who behind the attacks. Arafat "must do everything in his power to find those who murdered innocent Israelis and bring them to justice," said Bush. Secretary of State Colin Powell spoke with Arafat by phone, urging "sustained" action against militants.

Israeli officials blamed Arafat for failing to crack down on militants and promised new action. One Cabinet minister said Arafat should be expelled from the region.

Arafat's Palestinian Authority condemned the bombings, expressing its "deep anger ... and pain" and accusing the bombers of trying to derail a U.S. peace initiative.

In an emergency meeting, Arafat's leadership said it would take harsh action against militants. It declared a state of emergency in the areas under its control and said militant groups violating a long-broken cease-fire should consider themselves outlawed.

In Lebanon, Palestinian refugees in half a dozen camps fired machine guns into the air yesterday to celebrate the suicide attacks.

The European Union and European governments pressed Arafat to take action. Pope John Paul II, addressing pilgrims at St. Peter's Square, called news of the attacks "sorrowful and worrisome."

The attack in Jerusalem occurred just before midnight Saturday, when two suicide bombers detonated their explosives at the Ben Yehuda pedestrian mall. Ten people, most ranging from 14 to 20 years in age, were killed, along with the two suicide bombers, and more than 150 people wounded.

Around noon yesterday, the blast went off in Haifa in northern Israel.

Police officials said the Haifa bomber got on a city bus, paid his fare, then detonated explosives filled with nails.

"The bus came down the hill ... and as it leveled out it blew up," witness Rachel Antebe told Israel Radio. Another witness, Yaakov Vaknin, said he heard a loud blast. "I saw people flying through the air. I heard people screaming," he said.

The front of the red-and-white bus was twisted and burned, its roof buckled upward and sides blown out. Police explosives experts searched the inside of the bus, climbing over mangled seats.

Police said 15 people were killed in the bus, in addition to the bomber, while two pedestrians were crushed to death by the bus as it careened out of control. Rescue service spokesman Avi Zohar said about 40 people were wounded.

Hamas and Islamic Jihad had vowed revenge against Israel's killing nine days

ago of Hamas's Mahmoud Abu Hanoud, who Israel said had planned past bombings.

"The Palestinian people are adamant on continuation of resistance ... until the defeat of (Israeli) occupation, regardless of the price," Abdel Aziz Rantisi, a senior Hamas official, said.

Hamas also claimed responsibility for a shooting in the Gaza Strip yesterday in which two Palestinians fired on Israeli cars, killing one person and wounding five

others before soldiers shot them dead.

U.S. peace envoy Anthony Zinni, who since last week has been meeting leader from both sides in hopes of sending 14 months of violence, laid a wreath at the site of the Jerusalem attack.

Israeli officials said they were tired of waiting for Arafat to act.

Arafat does "not do anything about the fight against terrorism, and it's obvious that we will have to take this fight into our own hands," Israeli Foreign Ministry

spokesman Emmanuel Nahshon said.

Gideon Meir, a senior Foreign Ministry official, said there was "no question there will be a change in our policy."

In a first step, Israeli further tightened travel restrictions in the West Bank, barring cars with Palestinian license plates from driving on roads in areas under Israeli control. Troops also sealed all Palestinian-controlled towns, barring residents from leaving or entering.

In traditionally Arab east Jerusalem, an Israel guard shot and killed a Palestinian who the guard said tried to seize his weapon, police said.

Infrastructure Minister Avigdor Lieberman called for expelling Arafat and sending Israeli troops into Palestinian-controlled territory.

The bombs in Jerusalem went off around 11:30 p.m. Saturday, when the Ben Yehuda mall and its sidewalk cafes were crowded with young people. The two bombers were about 30 yards from each other, police said.

Witness Eli Shetreet said he saw bodies being hurled in the air. "A lot of people were crying, falling, and there was the smell of burning hair," said 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 afterward, an explosion went off in a car parked near the mall, causing no injuries.

Palestinian security officials said Israeli security arrested nine relatives of the bombers from their home village, Abu Dis, outside Jerusalem early yesterday. One of the bombers recently resigned from a Palestinian security service, the officials said.