Published July 30, 2014 • FoxNews.comFacebook242 Twitter528 livefyre3852 Palestinian authorities claimed that a United Nations school was hit by Israeli tank shells early Wednesday, resulting in the deaths of 15 people and injuring 90, while Israel announced a four-hour cease-fire for parts of the Gaza Strip. The Israeli military said it fired after its soldiers were targeted by mortars operating from the vicinity of the school. ADVERTISEMENT ADVERTISEMENT "In response, soldiers fired toward the origins of fire. And we're still reviewing the incident," the military said in a statement. The shelling came amid the heaviest air and artillery assault by Israel against targets in Gaza since the beginning of Operation Protective Edge earlier this month. On Wednesday afternoon, Israel’s military declared a four-hour cease-fire in some areas of the Gaza Strip, saying it's for humanitarian reasons. The cease-fire began at 3 p.m. local time. The cease-fire would not apply to areas of Gaza where the military is searching for tunnels used by Hamas militants, IDF Chief of Staff Lt.-Gen. Benny Gantz announced, according to the Jerusalem Post. Hamas spokesman Sami Abu Zuhri said it lacked any "value" because it excluded border areas from where Hamas wanted to evacuate the wounded. During the cease-fire, Gaza health officials said 15 people were killed and more than 150 wounded by an Israeli airstrike in a crowded shopping area. The Israeli military had no immediate comment. Gaza health official Ashraf al-Kidra said the area was busy Wednesday because residents thought a cease-fire was in place. The Palestinian Red Crescent confirmed the death toll. Earlier Wednesday, the IDF claimed it hit 75 sites, including five mosques it said were being used by militants to hide weapons and gain access to tunnels that extend into Israel. Hamas militants have used the tunnels to slip across the border between Israel and Gaza and attack Israeli soldiers and civilians. The IDF also claimed that it had destroyed three such tunnels in the previous 24 hours. In total, the Israeli army says that 32 tunnels have been located. However, it is not clear how many remain. Health officials in Gaza say that at least 1,284 people have been killed in the violence, with more than 7,100 wounded. It is not clear how many of the Palestinian dead are civilians and how many are militants. Israel has lost 53 soldiers and three civilians. Tank shells hit the U.N. school in the Jebaliya refugee camp early Wednesday, said Adnan Abu Hasna, a spokesman for the U.N. Relief and Works Agency. The agency is sheltering more than 200,000 people displaced by the fighting at dozens of U.N. schools in Gaza. Al-Kidra said at least 15 people were killed and about 90 wounded in the school strike. In all, 55 Palestinians were killed by airstrikes and tank shelling in different areas of Gaza on Wednesday, he added. Starting at around 4:30 a.m., several shells hit the compound of the Abu Hussein school, a few minutes apart, said the principal, Fayez Abu Dayeh. He said shells hit two classrooms and a bathroom. 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." In one of the classrooms, the front wall was blown out, leaving debris and bloodied clothing. Another strike tore a large round hole into the ceiling of a second floor class-room. About two hours after the strike, hundreds of people still crowded the courtyard, some dazed, others wailing. Aishe Abu Darabeh, 56, sat on the ground with her relatives, just a few meters from the destroyed classroom. "Where will we go?" she asked. "Where will we go next? We fled and they (the Israelis) are following us." Four of the dead were killed just outside the school compound, two in their home and two who were struck in the street after returning from pre-dawn prayers, their relatives said.