Tank fire has killed at least 15 Palestinians sheltering at a UN-run school in a Gaza refugee camp, the UN has said.

Israel, which has accused the militant group Hamas of using schools as bases to launch rockets, said it was investigating the reports.

Christopher Gunness from the United Nations Relief and Works Agency said the location of the school had been passed to the Israeli forces 17 times to ensure its protection.

He said the artillery attack on the school was ''an affront to all of us... a source of universal shame''.