U.N. Secretary-General Ban Ki-moon condemned a deadly attack on a Gaza school on Sunday as a "moral outrage and a criminal act" and demanded those responsible for the "gross violation of international humanitarian law" be held accountable.

The shelling of the U.N. school in Rafah in southern Gaza killed at least 10 civilians, the United Nations said. It was the third deadly attack on a U.N. school sheltering Palestinians during the 27-day Zionist onslaught.

All three incidents are being investigated, but the United Nations has initially blamed the Zionist entity for Sunday's attack and another strike last Wednesday on a U.N.-run school in Jabalya refugee camp that killed at least 15 civilians.
"The Israel Defense Forces have been repeatedly informed of the location of these sites," Ban's spokesman said in a statement.

"This attack, along with other breaches of international law, must be swiftly investigated and those responsible held accountable. It is a moral outrage and a criminal act," the statement said.

Ban again demanded an end to the fighting and for the parties to begin negotiations in Cairo to address the underlying issues of the conflict.

"The resurgence in fighting has only exacerbated the man-made humanitarian and health crisis wreaking havoc in Gaza," the statement said. "This madness must stop."