Thousands of Palestinians protesting against the fighting in Gaza clashed with Israeli soldiers as the violence spread to the West Bank.
At least one Palestinian was killed and dozens were injured in Qalandia, near the West Bank city of Ramallah, a Palestinian doctor said.
The violence came after a UN school in Gaza crowded with hundreds of Palestinians seeking refuge from fierce fighting came under fire yesterday, killing at least 15 civilians.
Palestinian officials blamed Israel for the shelling, which wounded dozens and came on the deadliest day so far of the current round of fighting.
However, the Israeli military said the school "was not a target in any way" and raised the possibility the compound was hit by Hamas rockets.
UN Secretary-General Ban Ki-moon angrily denounced the Gaza attack, saying the killing must "stop now".
But the frantic diplomatic efforts spanning the region were running into a brick wall. Israel demands that Hamas stop firing rockets without conditions, while Gaza's Islamic militant rulers insist the seven-year Israeli-Egyptian blockade of the territory must end first.
"Many have been killed - including women and children, as well as UN staff," Mr Ban said.
In the aftermath of the attack, a child's sandal decorated with a yellow flower lay in a puddle of blood, while sheep and cattle belonging to those seeking shelter grazed in the grass nearby.
A large scorch mark scarred the spot where one of the shells hit. Dozens of wounded, including many children, were wheeled into a nearby hospital as sirens wailed.
The UN said it had been trying to achieve a humanitarian pause in the fighting to allow the evacuation of civilians from the area.
Kamel al-Kafarne, who was in the school, said people were boarding buses when three tank shells hit.
"We were about to get out of the school, then they hit the school. They kept on shelling it," he said.
It was the fourth time a UN facility has been hit in Gaza fighting since the Israeli operation began on July 8.
UNRWA, the UN's Palestinian refugee agency, has said it discovered dozens of Hamas rockets hidden inside two vacant schools.
But UN spokesman Farhan Haq said the school hit yesterday in the northern town of Beit Hanoun was not one of hem.
The UN has also expressed alarm that rockets found in the schools have gone missing after they were turned over to local authorities in Gaza.
"Those responsible are turning schools into potential military targets, and endangering the lives of innocent children," UN staff and anyone seeking shelter there, a UN statement said.
Who launched the attack against the U.N. compound in Beit Hanoun also was under dispute.
The Palestinian Red Crescent said Israeli shells hit the school.
But Israel's chief military spokesman, Brigadier General Moti Almoz, said the military was investigating and it was too early to know if the deaths were caused by an errant Israeli shell or Hamas fire.
"We are not ruling out the possibility that it was Hamas fire," he said.
Fighting was fierce across Gaza yesterday, and at least 119 Palestinians were killed, making it the bloodiest day of the 17-day war. That raised the overall Palestinian death toll to at least 803, Gaza health official Ashraf al-Kidra said.
Israel has lost 32 soldiers, all since July 17, when it widened its air campaign into a full-scale ground war. Two Israeli civilians and a Thai worker in Israel have also been killed by rocket or mortar fire.
Israel says the war is meant to halt the relentless rocket fire on its cities by Palestinian militants in Gaza and to destroy a sophisticated network of cross-border tunnels that Hamas is using to sneak into Israel to try to carry out attacks inside communities near the border.
Israel insists it does its utmost to prevent civilian casualties but says Hamas puts Palestinians in danger by hiding arms and fighters in civilian areas.
The attack on Beit Hanoun was likely to increase pressure on international diplomats shuttling around the region in an effort to broker a cease-fire.
More than 2,300 rockets have been fired at Israel from Gaza since July 8, and the Israeli military says it has uncovered 31 tunnels leading from Gaza to Israel, some of which have been used by Hamas to try to carry out attacks inside Israel.