KFAR DAROM, Gaza Strip - Palestinians launched a bomb attack against a school bus Monday, killing two Israelis and wounding nine, and Israel retaliated with its most punishing airstrike in nearly two months of fighting. Helicopters and boats barraged the offices of Palestinian security forces in Gaza City with dozens of rockets.
The bus bombing in the Gaza Strip and the Israeli response dashed hopes that Israelis and Palestinians might be moving toward a truce and a resumption of peace talks. The fighting has left some 240 people dead since Sept. 28, mostly Palestinians.
''We will continue to work with all our might to stop the violence, and make the Palestinian Authority understand that it will not achieve anything with violence,'' Israeli Prime Minister Ehud Barak said Monday night.
He blamed the bus bombing - in which five of the nine wounded were children - on the Tanzim militia, which is connected to Palestinian leader Yasser Arafat's political movement, Fatah.
Palestinian officials said 62 people were injured in the Israeli bombardments, about half of them civilians.
Israeli helicopters unleashed an hour-long rocket barrage at nightfall, targeting Fatah and Palestinian security offices, including police headquarters and a building not far from the office where Arafat was working at the time.
The airstrike cut electricity, plunging Gaza City into darkness, and rockets hit several nearby refugee camps, witnesses said. At least 22 of the wounded were from Shati camp, doctors said. Israel said missile boats off the Gaza coast in the Mediterranean joined the attack.
Many of the offices targeted were under the control of Mohammed Dahlan, head of the Preventive Security Service, who Israeli television said was suspected in the bus attack.
After the Israeli assault, Dahlan was defiant. He told Associated Press Television News the Palestinians will confront Israel until ''Palestinian national rights are achieved.''
Arafat's aides denounced the bus attack. ''We had nothing to do with this incident. We reject any kind of violence,'' said Arafat adviser Nabil Aburdeneh.
The White House called for ''clear and unambiguous'' condemnations of the bus attack and urged the Palestinians to arrest the bombers.
''It's important that there be a clear condemnation of the attack,'' national security spokesman P.J. Crowley said. ''As long as the violence continues, we have great concern that this could spiral out of control.''
The school bus was hit shortly after it left the isolated Jewish settlement of Kfar Darom in the heart of the Gaza Strip at around 7:30 a.m. Students and teachers were en route to elementary school in Gush Katif, a bloc of Jewish settlements in the southern Gaza Strip.
The bomb blast, from a 155 mm mortar shell attached to an explosive device, tore melon-sized holes in the red-and-white bus and shattered its windows.
The Israeli military said three Palestinians set off the bomb several dozen yards from the bus and fled on foot into Palestinian-controlled territory.
The words, ''This is what we get for restraint,'' were spraypainted in Hebrew on the wrecked bus after the blast.
Three of the injured children were siblings. Orit Cohen, 12, lost her right foot, her younger brother, Israel, 7, lost part of one leg and her younger sister, Tehila, 9, suffered serious wounds to both legs.
''I never imagined that we would have to pay such a heavy price for safeguarding our homeland,'' said Noga Cohen, the children's mother.
About 6,500 Jewish settlers live among more than 1 million Palestinians in Gaza. The settlers in Gaza and the West Bank have been a frequent target for attack since the violence erupted.
Three groups - Palestinian Hezbollah, Al-Aqsa Martyrs and Omar Al-Mukhtar - claimed responsibility for the bus attack. The first two have not been active before. The third, Damascus-based Omar Al-Mukhtar, is a splinter of a PLO faction.
The leader of Hamas, a militant group that has conducted past bombings, was evasive when asked whether his group was responsible. ''What happened today is a natural outcome of the many deaths on the Palestinian side,'' Sheik Ahmed Yassin said. ''Our targets are not children, but the military.''
Last week, Arafat ordered Palestinians to stop shooting at Israelis from areas under Palestinian control. However, the ban did not refer to attacks in areas of the West Bank and Gaza that remain under Israeli control. The bus was traveling on a road that is Israeli controlled.
Palestinians cleared out of the security offices shortly before the raids began. In previous strikes, Israel gave the Palestinians advance notice to avoid casualties. It was not clear if a warning was given this time.
Helicopters struck two offices in the Jabaliya camp, said Palestinian reporter Abdul Khader Hamad. ''They shot more than 20 rockets into Jabaliya camp,'' he said. ''We saw everything.'' There were no reports of injuries at the camp.
Israeli forces also closed a strip of Gaza territory from the border to the seacoast, preventing Palestinians from traveling from the northern half of Gaza to the southern half. Already in force were bans on import of fuel and most other products, except food and medicine.
''It is a new declaration of the aggressive war against the Palestinians,'' said Palestinian negotiator Hassan Asfour. ''The killers ... will pay the price,'' he said, mentioning Barak, Foreign Minister Shlomo Ben-Ami and army chief Lt. Gen. Shaul Mofaz by name.