A suicide bomber detonated a powerful explosive aboard a crowded bus in the residential hills of this Mediterranean port city Wednesday, setting off a fiery blast that killed at least 15 passengers, along with the bomber, and injured more than 40 in the first such attack in Israel in two months.

Just after midnight this morning, Israeli military forces invaded a refugee camp in the northern Gaza Strip. Merkava tanks and AH-64 Apache helicopters opened fire on gunmen and civilians, killing 11 Palestinians, including a 60-year-old man, and injuring more than 140, according to witnesses.

The suicide blast Wednesday tore off the roof of the bus, leaving it a twisted, charred wreck, and spewed blood and body parts across a wide boulevard. Workers using cherry pickers spent the afternoon removing body parts from the upper branches of nearby trees. On the pavement, black with soot from a smoky fire that engulfed the bus, rescue workers found dozens of dead and wounded people lying on a carpet of shattered glass, bloody clothing and other debris. Police said the bomb was packed with shards of metal, nuts and bolts to increase its deadliness.

"I looked in the mirror to close the doors after the last passenger got off and suddenly there was an explosion," the bus driver, Marwan Damouni, 31, said while being treated at the Carmel Medical Center for injuries to his ears and hands.

"The bus was in ruins. I saw bodies, blood. I can't describe it," said Damouni, an Israeli Arab. "Everything inside was scattered. Everything was broken. There were bodies in the aisle, bodies in the staircases, bodies on the seats. I couldn't look anymore, and I got out of the place."

Many of the victims were high school students, including Avigail Elizabeth Litle, 14, a U.S. and Israeli citizen who lived in Haifa, according to Israeli authorities. At least five other teenagers and two Israeli soldiers also died.

In the Gaza Strip today, Israeli forces launched their second tank and helicopter attack this week, killing 11 Palestinians in the Jabalya Refugee Camp in what an Israeli military spokesman called a "massive exchange of gunfire" during a seven-hour operation.

The military spokesman said the target of the Israeli attack, which involved about 30 to 50 armored vehicles, was the destruction of two buildings -- the home of an alleged militant and a workshop that the Israeli military said was used to make weapons.

Palestinian witnesses said the tanks and helicopters opened fire on crowds of civilians in the streets. Two journalists reportedly were injured, witnesses said.

The previous suicide attack in Israel was a double bombing Jan. 5 in Tel Aviv. Two Palestinians detonated themselves almost simultaneously about 200 yards apart, at a bus stop and on a crowded pedestrian boulevard, killing 25 people, including themselves, and injuring more than 100.

The 59-day lull was unusually long for the 30-month-old Palestinian uprising, a hallmark of which has been suicide bombings by radical Palestinian groups to fight Israel's continuing occupation of the West Bank and Gaza Strip. But Israeli officials said the pause did not reflect a change in tactics by the Palestinian groups but, rather, resulted from tough Israeli attacks in Palestinian areas to protect its citizens.

"It has not been calm these last two months. There have been over 57 interceptions this last month" of would-be Palestinian attackers by Israeli military and security forces, said an Israeli Foreign Ministry spokesman, Jonathan Peled. Most were suicide bombers, he said, adding that since the outbreak of the Palestinian uprising in September 2000, more than 315 people -- most of them Israeli citizens, settlers and soldiers -- have been killed in 68 suicide bombings.

"The question is, with all these victims, are they going to bring the Palestinians statehood or end corruption or alleviate Palestinian suffering?" he asked. "As we say, peace starts where terrorism ends."

The White House spokesman, Ari Fleischer, said in Washington on Wednesday that President Bush "condemns in the strongest terms today's attack on innocents in Israel. His message to terrorists is that their efforts will not be successful."

No group asserted responsibility for the blast in Haifa. The spokesman for Yasser Arafat's Palestinian Authority, Yasser Abed Rabbo, condemned the attack, saying the Palestinian leadership opposed "all attacks against civilians" and adding that the blast Wednesday would "only serve to distract attention from the more than 150 Palestinian civilians killed by Israel over the last two months."

The Israeli police spokesman, Gil Kleiman, said police believe that an identification card found on the scene belonged to the suicide bomber. The card, found near the presumed bomber's body, carried the name Mahmoud Amdan Salim Kawasme, 20, of the West Bank city of Hebron, Kleiman said. Police also found a letter in Arabic near the body that "praises the terror attacks on the twin towers on September 11," Kleiman said.

The letter claimed that the Islamic holy book, the Koran, foretold that the towers at the World Trade Center in New York and people near Ground Zero would collapse into hell. The second page of the letter contained a prayer that the bomber presumably recited to protect himself from capture prior to carrying out the bombing in Haifa.

Israeli soldiers detained the father and two brothers of the suspected bomber at their Hebron home late Wednesday on suspicion of involvement in the attack, according to a military spokesman.

In at least four West Bank cities -- Nablus, Jenin, Tulkarm and Qalqilyah -- small groups of young Palestinians burst into spontaneous celebrations of joy, whistling, honking car horns and shouting support for the attack. Journalists and residents interviewed by phone said the youths said they backed the bombing because Israel continued military actions against Palestinians despite two months without a suicide attack.

The bombing came less than a week after the swearing-in of a new Israeli government under Prime Minister Ariel Sharon that is expected to adopt a harder line against Palestinian terrorism and against reopening negotiations to end the conflict, which has claimed more than 2,000 Palestinian and 700 Israeli lives.

Since four Israeli soldiers were killed Feb. 15 when their tank drove over a land mine in the Gaza Strip, the Israeli military has waged an aggressive campaign against the militant Islamic Resistance Movement, or Hamas, in Gaza, killing dozens of Palestinian militants and civilians. Hamas has asserted responsibility for the tank attack and for firing numerous homemade rockets -- usually without injury or serious damage -- at Israeli communities just outside the Gaza Strip.

Israeli police said the blast occurred about 2:15 p.m. on Egged Bus No. 37, which begins its route at a station near the coastline of Haifa, on the sea about 50 miles north of Tel Aviv. It passes near the University of Haifa and circles through residential communities that cling to the wooded slopes of Mount Carmel. The red-and-white striped vehicle was headed south and had just arrived at a bus kiosk on Moriya Boulevard -- a main north-south thoroughfare through the neighborhood of Carmelia -- when the blast occurred.

"I thought the war had started," said Alma Silikov, 85, who lives in an apartment building next to the bus stop, which had all its windows shattered and its aluminum shutters shredded.

Odette Elezra, 51, a nanny, was waiting for a bus at the stop on the opposite side of the street when she heard the blast.

"I looked back and saw the bus burning," said Elezra, who suffered cuts and bruises on both legs. "I saw bodies, bodies flying -- it was horrible. I can't believe I'm alive."

"We saw people lying in the street who had flown out of the bus," said the deputy commander of the Haifa fire department, Eliyahu Emil, who heard the explosion at his firehouse a few blocks away and arrived at the scene minutes later.

Emil speculated that the bomber may have detonated his explosives shortly after boarding through a door near the center of the vehicle, because that was where the damage was most severe and because the lower half of a body was lying on the ground just outside the door.

"I thought it was an earthquake. I heard a very strong boom!" said Miriam Attar, 71, who lives in the apartment building next to the bus stop. She went to the window to see what had happened. "I saw the heads of kids hanging out the windows of the bus," she said.

Anderson reported from Jerusalem. Researcher Samuel Sockol contributed to this report.

Investigators pick up pieces of evidence from the bombing scene in the coastal city of Haifa. The attack broke a two-month lull in suicide attacks. Mazal Yaakov watches over her sister, Sol Tzur, who was injured in the bombing, at a medical center in Haifa.