Update 2:02 p.m. ET

The State Department joined United Nations Secretary-General Ban Ki-moon in condemning the killing of 10 Palestinians outside of a UN Relief and Works Agency school in Gaza on Sunday, as the Israeli military issued a warning to residents of the Palestinian territory that “the battle is ongoing.”

“The United States is appalled by today’s disgraceful shelling outside an UNRWA school in Rafah sheltering some 3,000 displaced persons,” said State Department spokesperson Jen Psaki, in a statement issued Sunday. “The coordinates of the school, like all UN facilities in Gaza, have been repeatedly communicated to the Israeli Defense Forces. We once again stress that Israel must do more to meet its own standards and avoid civilian casualties.” She called for a “full and prompt” investigation of the incident.

In a statement earlier Sunday, UN chief Ban Ki-moon called the attack “a moral outrage and a criminal act.” Ban also called for an investigation into what he called “yet another gross violation of international humanitarian law,” and for an immediate end to fighting. “This madness must stop,” he said.

The school had been sheltering Gaza residents displaced by the nearly four weeks of fighting that have taken place. Approximately six UN facilities have been hit by Israeli fire since the conflict began, the Associated Press reports. The Israel military had no immediate comment on the most recent attack, but said it would look into the reports.

Israel has previously said that when Hamas deliberately uses civilian centers as weapons depots or places from which to fire rockets, it turns those places into targets. “When a schoolhouse, hospital, mosque is turned into a military command center or a weapons depot, or a place where you fire rockets, it becomes by the rules of war a legitimate target,” said Ron Dermer, the Israeli ambassador to the United States, on July 22.

As the UN called for an immediate end to the violence, the IDF began withdrawing some troops from the Gaza strip as it entered a “next stage” of combat. A statement from the IDF says it was “redeploying to enable combat against Hamas & continued defense from tunnels.”

“We have indeed scaled down some of the presence and indeed urged Palestinians in certain neighborhoods to come back to their homes,” military spokesman Lt. Col. Peter Lerner also told the AP, though Israeli air strikes continue in the region.

The IDF shared its plans to scale back troop numbers as it dropped notices all over the Gaza Strip warning that “the battle is ongoing” and that “all the leaders of Hamas and other terrorist groups are unsafe,” NBC News reports.

Israeli Prime Minister Benjamin Netanyahu said in a Saturday evening press conference that Israeli’s Operation Protective Edge would go on in Gaza “no matter how much time it takes and how much strength it requires,” the Jewish Telegraphic Agency reports.

“Every option is on the table to ensure long-term quiet to the residents of Israel,” Netanyahu said. “I won’t say when we’ll finish and where we’ll go. We have no obligation outside of our security concerns.”

Plans for a 72-hour cease-fire brokered by the UN and U.S. Secretary of State John Kerry fell apart Friday morning just before the truce was supposed to begin, reportedly after a Palestinian militant made a suicide-bomb attack near the town of Rafah.

More than 1,750 Palestinians, largely civilians, and 70 Israelis, mostly soldiers, have been killed in the conflict so far.

Related: Children Suffer as War Continues in Gaza and Israel

Write to Nolan Feeney at nolan.feeney@time.com.