JERUSALEM (AP) -- In back-to-back attacks early Tuesday, a Palestinian man opened fire on a crowded Tel Aviv nightclub, a suicide bomber blew himself up on an Israeli bus and gunmen ambushed Israeli motorists in the West Bank. In all, five Israelis and two Palestinian assailants were killed.

Also Tuesday, a bomb went off in the yard of an Arab high school, lightly injuring seven students and a teacher. Israeli media said a previously unknown group, apparently consisting of Jewish extremists, claimed responsibility.

And in the Gaza Strip, 15 Palestinians were wounded, three of them seriously, when an explosion -- apparently caused by a bomb that went off prematurely -- rocked a building under construction in a residential area of Gaza City.

The cycle of attacks and reprisals was one of the bloodiest in 17 months of fighting. Palestinian militants vowed to avenge recent Israeli military strikes, including shelling that killed five Palestinian youngsters Monday. Sheik Ahmed Yassin, founder of the Islamic militant Hamas group, said attacks would continue "until the full liberation of Palestine."

Ahmed Abdel Rahman, an aide to Palestinian leader Yasser Arafat, said the Israeli strikes were a `very serious escalation" and called for U.N. intervention.

Israeli Prime Minister Ariel Sharon, meanwhile, told reporters the Palestinians would have to be hit hard to understand that Israel will not succumb to violence.

"We will wage a relentless war against terrorism, because for us it's a question of survival," said Israeli government spokesman Avi Pazner, adding that negotiations with the Palestinians could only resume once Israel won that war.

Israel's security Cabinet met Tuesday to assess the army's response, and Sharon reportedly proposed tightening the cordon of tanks near Arafat's headquarters in the West Bank town of Ramallah.

In reprisals late Monday for previous attacks, Israeli warplanes, helicopters and navy gunboats attacked Arafat's offices in Ramallah, the West Bank town of Bethlehem and in Gaza City. One missile hit several yards from the Ramallah office where Arafat was with his aides, but he was not harmed. On Tuesday morning, Israeli helicopter gunships fired missiles at Palestinian security headquarters in the town of Khan Yunis in the Gaza Strip, causing severe damage. One man was wounded.

Tuesday's violence began at around 2:15 a.m. when a Palestinian gunman armed with grenades, a knife and an M-16 assault rifle opened fire on the Seafood Market, an all-night restaurant and nightclub in a commercial district of Tel Aviv, where a group of women was attending a bachelorette's party.

The bride-to-be, Irit Rahamim, said that when the first shots went off, she and her friends dove to the ground. "At one point, there was quiet, and I told all my girlfriends, `Let's run away from here,"' Rahamim told Israel TV's Channel Two. She said her friends forced her to stay down. "It's good they did, because after that, there was more shooting."

Another witness said that at one point the assailant hurled a grenade that rolled onto the dance floor but did not go off. Three Israelis, including a policeman, were killed in the attack, and 31 were injured.

There were conflicting reports on how the assailant was killed. One of the patrons, William Hazan, said he fired at the attacker who at the time was stabbing another guest. Police said officers killed the assailant.

The Al Aqsa Brigades, a militia linked to Arafat's Fatah movement, claimed responsibility for the shooting. The assailant was identified as Ibrahim Hassouna, 20, an officer in the Palestinian naval police and a resident of the Balata refugee camp near the West Bank town of Nablus.

On Tuesday morning, a suicide bomber blew himself up on a bus in the main station in the central Israeli town of Afula, killing himself and an Israeli passenger and wounding 11 people, police said. Bus driver Danny Nahum said the man was wearing a heavy coat when he boarded the bus and at first did not want to accept the change after paying his fare. Nahum said the man sat next to the back door, and set off the explosives as the bus pulled into the Afula station.

Also Tuesday, Palestinian gunmen fired at Israeli motorists on the West Bank's main north-south highway, just south of Jerusalem. An Israeli woman was killed and her husband was lightly injured. Israeli troops returned fire. Several hours later, there was another shooting attack in the same spot, lightly injuring a reporter for Israel TV, Benny Lis.

In the Arab neighborhood of Tzur Baher, a bomb went off in a high school Tuesday morning, injuring seven students and a teacher. In Hebrew-language messages sent by beeper to Israeli radio stations, a group calling itself "The Avengers of the Infants" claimed responsibility.

Jerusalem Mayor Ehud Olmert arrived at the scene, and was met by chants of "out, out" from the students. After Olmert left, several students threw stones at police who responded with tear gas and stun grenades. Police said eight officers were lightly hurt.

There was speculation that the school bombing came as reprisal for a suicide bombing in Jerusalem on Saturday in which 10 Israelis, including five infants and children, were killed.

In the past four days of fighting, 32 Palestinians and 27 Israelis have been killed, one of the sharpest escalations since violence erupted in September 2000.

Egyptian President Hosni Mubarak was to meet with President Bush at the White House on Tuesday to discuss his proposal to host an Israeli-Palestinian summit meeting with Secretary of State Colin Powell.

Powell called it "an interesting idea," but said a decision ultimately was up to Sharon and Arafat. Powell said the Mideast situation had become "terrible" because of escalating violence, and that the Bush administration was redoubling its efforts to halt the strife.