Israeli attacks on three schools run by the United Nations in the Gaza Strip in the last 24 hours, including one that killed more than 46 civilians Tuesday, were "totally unacceptable and must not be repeated," UN Secretary General Ban Ki-moon said.

The three schools were operated by the UN Relief and Works Agency for Palestinian Refugees in the Near East (UNRWA) in Gaza. The UN said about 15,000 Palestinians, who fled the fighting between Israel and Hamas, had found refuge in these schools as well as in more than 20 other schools in the territory.