GAZA CITY, Gaza Strip — Israeli tank shells tore through the walls of a UN school crowded with war refugees early Wednesday in the deadliest of a series of air and artillery attacks.
Hours later, Israeli strikes hit a crowded shopping area in Gaza City. The bloodshed followed an escalation by both sides fighting in the coastal territory, further dimming prospects for a sustainable cease-fire despite international diplomatic efforts.
The attack on the UN school in the Jebaliya refugee camp was the second deadly strike on a UN compound in a week. Shells slammed into the compound before dawn, said Adnan Abu Hasna, a spokesman for the UN Relief and Works Agency, which is sheltering about 200,000 people displaced by the fighting at dozens of UN schools across Gaza.
Gaza health ministry official Ashraf al-Kidra said at least 17 people were killed and about 90 wounded in the school strike.
The Israeli military said it fired back after its soldiers were targeted by mortar rounds launched from the vicinity of the school.
Assad Sabah said he and his five children were huddling under desks in one of the classrooms because of the constant sound of tank fire throughout the night.
‘‘We were scared to death,’’ he said. ‘‘After 4:30 a.m., tanks started firing more. Three explosions shook the school.
‘‘One classroom collapsed over the head of the people who were inside,’’ he said.
In one classroom, the front wall was blown out, leaving debris and bloodied clothing. Another strike tore a large round hole in the ceiling of a second-floor classroom.
Hundreds of people crowded the school courtyard after the strike, some dazed, others wailing.
‘‘Where will we go?’’ asked Aishe Abu Darabeh, 56. ‘‘Where will we go next? We fled, and they are following us.’’
In all, 1,361 Palestinians have been killed — 116 on Wednesday — and more than 7,600 wounded since the July 8 start of fighting, Kidra said. The Israeli military said three of its soldiers were killed when a booby-trapped house collapsed after they identified an entrance to a tunnel inside, raising to 56 the number killed since a ground war began earlier this month. Three civilians also have been killed on the Israeli side.
The United Nations said it was the sixth school to be hit since the conflict began, and the second at which fatalities occurred. At least 15 civilians were killed last Thursday when the courtyard of a UN school in Gaza City was hit. Israel has acknowledged that troops fired a mortar shell that hit the courtyard, but it said aerial footage shows that the yard was empty at the time, and that the shell could not have killed anyone.
UN Secretary General Ban Ki-moon called Wednesday’s strike ‘‘outrageous’’ and ‘‘unjustifiable,’’ and demanded an immediate humanitarian cease-fire in the war.
‘‘Nothing is more shameful than attacking sleeping children,’’ Ban said on his arrival in Costa Rica. He added that ‘‘all available evidence points to Israeli artillery as the cause’’ and noted that Israeli military authorities had received the coordinates of the school from the United Nations 17 times, including on Tuesday night.
Responding to Israeli statements that its soldiers were responding to rocket fire from near the school, the UN deputy secretary general, Jan Eliasson, drew attention to the Geneva Conventions, which in laying out the rules of war unequivocally prohibit attacks on schools and hospitals.
“This is a moment where you really have to say, ‘Enough is enough,’ and you have to search for the right words to convince those who have the power to stop this,” Eliasson said.
The White House also condemned the deadly shelling but did not assign blame. White House spokeswoman Bernadette Meehan also said the United States is ‘‘extremely concerned’’ that thousands of Palestinians are not safe in UN-designated shelters, despite being told by Israel’s military to leave their homes. Israel has been warning civilians by phone and leaflet to leave dangerous areas ahead of strikes on militant targets.
The mortar shells were fired from a distance of some 200 yards from the school, said an Israeli military official, speaking on condition of anonymity because he was not authorized to talk to the media.
Yomtov Tamir, a retired Israeli general, said he was not familiar with Wednesday’s strike but said that even though tank fire is generally ‘‘very accurate’’ it can miss its target for a variety of reasons.
‘‘One, it might have gone through a target,” he said. “Two, it might be a mistake in identification, that they intended to hit something specific, but that it was actually something other than what the person aiming intended.’’
Hours later, several Israeli shells hit a crowded shopping area in the Shijaiyah district in Gaza City, killing at least 16 people, including local Palestinian photographer Rami Rayan, who was wearing a press vest at the time, and wounding more than 200 people, Gaza health officials said.
Kidra and witnesses said the shopping area was busy because residents, and many who had taken shelter in the area from fighting elsewhere, thought a cease-fire was in place.
The Israeli military had no immediate comment on the strike on the shopping area, saying it was investigating the report.
Gaza militants fired 84 rockets at Israel Wednesday, including more than 26 after the cease-fire was announced, the military said.