Photograph by Mustafa Hassona/Anadolu Agency/Getty.

After another day of carnage in the Gaza Strip, some details remain unclear. Was it an Israeli tank shell, or several of them, that killed at least ten people Thursday, and wounded scores more, at a school in the city of Beit Hanoun, which the United Nations was using as a temporary shelter for displaced civilians? (There are now a hundred and forty thousand people taking refuge in various U.N.-run schools.) Palestinian officials and U.N. representatives initially said that Israeli tank fire was responsible. But the Israel Defense Forces denied that they had targeted the school, and suggested that rockets fired by Hamas could have fallen short and done the damage.

Eyewitnesses said that several tank shells had hit the school and the area around it. “Pools of blood soiled the school courtyard, amid scattered books and belongings,” an A.P. report said. “There was a large scorch mark in the courtyard marking the place where one of the tank shells hit.” At the Kamal Adwan hospital, where some of the wounded were taken, a survivor of the explosions told a reporter from Al Jazeera, "We were sitting in the school because we were told it is safe. By God, there was not a single fighter; not a single shot was fired from the school. Why did they shoot at the school? Why? Can someone explain that to me? Why would they shell the school?"

As the day unfolded, Israeli officials pushed back against these accounts. According to a report in the Times, Peter Lerner, an Israeli military spokesman, said, “We have decisive information that several projectiles launched from within Gaza struck in Beit Hanoun between 2 o’clock and 4:15”—around the time the explosions at the school took place, suggesting that one or more of them may have been to blame. (Beit Hanoun is on the northeast edge of the Gaza Strip, close to the border with Israel.) The Times also quoted Brigadier General Michael Edelstein, the commander of the Gaza division, saying that he wasn’t yet sure what had happened. “If we made a mistake, we will say it,” Edelstein said, adding that Israel wouldn’t intentionally target U.N.-run facilities. “We would never bomb such a place,” he said.

The school in Beit Hanoun was one of more than eighty that the United Nations Relief and Works Agency is operating as shelters for civilians in Gaza who have fled from their homes to escape the bombing. In a series of tweets, Chris Guinness, a spokesman for UNRWA, said that, as fighting approached the school on Thursday, its representatives on the ground tried to negotiate safe passage for the hundreds of people it was harboring. "Precise co-ordinates of the UNRWA shelter in Beit Hanoun had been formally given to the Israeli army,” Guinness wrote. “Over the course of the day UNRWA tried to coordinate with the Israeli Army a window for civilians to leave and it was never granted."

In the past, Israel has claimed that Hamas was using some of the U.N.-operated schools as sites to launch rocket attacks. UNRWA denies this, but it has acknowledged finding rockets in a couple of vacant schools. In a tweet earlier on Thursday, Guinness wrote, “Meanwhile discovery of 2 rocket caches in UNRWA schools which we also strongly condemned illustrating neutrality violations on other side.” [Update: On Wednesday, Ban Ki-moon, the U.N. Secretary General, issued a statement saying that he was alarmed to learn that rockets were placed in a vacant U.N.-run school in Gaza. “Those responsible are turning schools into potential military targets, and endangering the lives of innocent children,” the statement said. Ki-moon’s spokesman, Farhan Haq, said the rockets had been turned over to the Palestinian authorities but now “have gone missing.”]

This is not the first time since the start of the Israeli ground offensive, which on Thursday entered its seventh day, that a U.N.-operated facility has been hit by munitions that appeared to have come from Israeli tanks. On Monday, according to Guinness, a school sheltering three hundred people was struck, and “when we went back 2 investigate there was more Israeli incoming.” On Tuesday morning, an “UNRWA Girl’s School in Deir Al Balah, central ‪#Gaza (sheltering 1,500) took a hit from Israeli fire, 5 injured.”

Exactly what happened in Beit Hanoun will be disputed for some time, most likely. But with the civilian-casualty toll growing every day, the latest tragedy illustrates the desperate need for a ceasefire. In the past twenty-four hours alone, according to Haaretz’s live blog of the conflict, eighty-four Palestinians have been killed, including six members of one family, who died when Israeli forces bombed one of their neighbors’ homes. Reuters reported that, on Thursday, the over-all death toll since the start of Operation Protective Edge now includes seven hundred and fifty-five Palestinians and thirty-two members of the Israel Defense Forces.

Alarmingly, hopes for a ceasefire faltered on Thursday. Secretary of State John Kerry left a meeting with Benjamin Netanyahu without securing an agreement. According to a report in the Washington Post, Netanyahu was furious about a ban on commercial airliners landing in Tel Aviv that the Federal Aviation Administration imposed earlier this week, suspecting that “it was an attempt by the Obama administration to squeeze Israel to end its Gaza campaign.” The flight ban was lifted on Thursday night, but Israel and Hamas gave no indication that they were ready to reach a deal. A senior official for Hamas reiterated that it wouldn’t halt its rocket attacks until Israel agreed to end its blockade of Gaza. Meanwhile, Moshe Ya'alon, Israel’s defense minister, told troops preparing to enter the Strip that the I.D.F. was on the verge of broadening its offensive. “We are preparing the next stages of the fighting after dealing with the tunnels, and you need to be ready for any mission,” Yaalon told the soldiers, according to the Post. “You need to be ready for more important steps in Gaza, and the units that are now on standby need to prepare to go in.” After Thursday’s tragic strike, where can Gaza residents take shelter?

[Update, 10 P.M.: On Thursday night, a spokesperson for the Israel Defense Forces put out a statement via Twitter that came close to conceding that the deaths at the school were the result of an Israeli strike. “In recent days, Hamas has fired rockets from an area of Beit Hanoun where an UNRWA shelter is located,” the I.D.F. tweets said. “Last night, we told Red Cross to evacuate civilians from UNRWA's shelter in Beit Hanoun btw 10 am & 2 pm. UNRWA & Red Cross got the message. Hamas prevented civilians from evacuating the area during the window that we gave them. Today Hamas continued firing from Beit Hanoun. The IDF responded by targeting the source of the fire.” This statement conflicts with the account of the attempted evacuation given by U.N. officials.]