Palestinians carry the body of a man, whom medics said was killed by Israeli shelling near a market in Shejaia as smoke rises, in the east of Gaza City July 30, 2014. REUTERS/Ashraf Amrah

GAZA CITY, Gaza -- A four-hour humanitarian cease-fire proposed by Israel fell apart quickly Wednesday evening when an Israeli bombardment of the Shejaiya district left more than 17 dead and 200 wounded, according to the Gaza Health Ministry, though several other Hamas officials claimed the number of people killed was much higher. The IsraeliDefense Forces (IDF) claimed that Hamas fired 26 rockets into southern Israel during the cease-fire, which was initially supposed to last from 3 p.m. to 7 p.m.

The attack on Shejaiya, which also killed one Palestinian journalist, came on the heels of another attack on a United Nations shelter Wednesday morning at a school in Jebaliya, which killed at least 15 people and wounded 90. Victims in both attacks included children. Combined, the blasts made Wednesday one of the bloodiest days since the beginning of the conflict earlier this month and stretched the limits of humanitarian aid organizations and Gazan hospitals.

“We have reached the end -- the limit,” United Nations Relief and Works Agency (UNRWA) spokesman Chris Gunness said during an interview Wednesday. “We are at the breaking point. Soon hundreds of thousands will be left out on the streets.” At the beginning of the conflict, UNRWA said in a statement that it was only able to handle shelter for 50,000 people. It is now providing assistance, including shelter, to more than 200,000. The Gaza Strip has a population of 1.8 million people.

The school in Jabaliya hosted about 3,300 people and was hit by three Israeli blasts in the early hours of Wednesday, according to a statement released by UNRWA Commissioner-General Pierre Krahenbuhl. Gaza's Health Ministry put the death toll at 15 while doctors at Al-Shifa Hospital in Gaza City said as many as 20 had died. UNRWA said it could not confirm a final death toll. The IDF has yet to officially comment on the incident.

“The precise location of the Jabalia Elementary Girls School and the fact that it was housing thousands of internally displaced people was communicated to the Israeli army seventeen times,” the statement said. Gunness said in an interview Wednesday that the organization had completed its investigation and determined that there were no Hamas rockets in the school or Hamas fighters nearby.

Following the blast in Jabaliya Wednesday morning, Nasser Khafja sat outside a damaged classroom and held a bandage on his chin. He had been hit with pieces of shrapnel just hours earlier. He said it took UNRWA senior staff and ambulances nearly one hour to reach the school. UNRWA security guards were on the scene and one of them was killed in the blast.

Khafja said he heard three blasts from his classroom at the U.N. shelter in Jabaliya early Wednesday morning: one hit the homes behind the complex, one the front gate, and one that landed directly in front of him. With the third blast, the electricity in the school shut off, and debris and mangled bodies flew into the air, he said.

“I was sleeping and then I went to the bathroom. On my way back I heard the rockets, and then the ceiling fell through,” Khafja said. “I stumbled over the dead bodies. I couldn’t see anything.”

Thousands of Palestinians stood in the courtyard of the school shelter in Jabaliya Wednesday morning, surveying the damage from the artillery fire. The side of two classrooms’ roofs had fallen through, the walls blown out. Outside the front entrance, dead horses, cut open from the shrapnel, were piled on top of each other in a wooden feeding pen. The attack on the school in Jabaliya was the second deadly blast to hit a UNRWA shelter in just one week.

The last attack on a UNRWA school July 24 in Beit Hanoun killed 15 people and left 200 injured. UNRWA spokesman Chris Gunness claimed that the attack was the result of Israeli artillery fire. The IDF denied that claim and said Hamas rockets were responsible for the destruction. Gunness said in tweets July 28 that UNRWA would continue to gather evidence about the attack. Since the beginning of the conflict, six UNRWA shelters have been hit, according to the organization.

Gunness said there is a possibility that members of the U.N. Mine Action Service, a group that deals with landmines and explosive remnants of war, will come into Gaza to ensure that Hamas does not hide rockets in UNRWA schools.

Most of the victims of Wednesday’s attack on the UNRWA school were transported to Kamal Odwan Hospital, which has been under fire several times throughout the conflict. Said Abu Ata, a doctor and administer of Kamal Odwan, said that since Tuesday 50 people had been killed in the area and since 1 a.m. Wednesday, 28 people had been killed and 176 injured. The hospital, she said, was at its maximum capacity.

Dr. Ashraf Qedra, a spokesman for Al-Shifa hospital in Gaza City, said his hospital was at 95 percent capacity.

“Many patients sleep on the floor,” he said, adding that the hospital is receiving donations from organizations in the West Bank and various Arab countries. Al-Shifa is funded by Hamas, he said, but the doctors have not been paid in three months.

Al-Shifa hospital experienced another influx of patients Wednesday evening after the attack in Shejaiya. Around 6 p.m. ambulances, blaring their sirens, sped into the back alley behind the hospital and stopped in front of the morgue. Hundreds of people gathered outside, watching men carry dead bodies into the building in body bags and place them inside large metal refrigeration boxes.

The bodies slid in on metal trays, stacked on top of one another. Young men crowded around the boxes, searching for family members, some falling to the ground, crying in the pools of blood left from transporting the bodies in and out of the building. In a side room next to the refrigeration boxes, doctors tended to two children, Abdel Azi, 3, and Halim, 5, who both died from injuries sustained in the Shejaiya blast.

"This is a real massacre," Hamas spokesperson Fouzi Barhum said. "Israel never had the intention of implementing a cease-fire. This massive killing just shows that the occupation needs regional and international attention."

The IDF said that three Israeli soldiers were killed Wednesday. A tweet from the IDF Wednesday night said sounds of rocket fire could be heard in central Israel.

According to Reuters, U.N. Deputy Secretary-General Jan Eliasson told a group of reporters at the U.N. Wednesday that the fighting in Gaza had gone too far.

"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," she said.