US says Israeli attack on UN school in Gaza is 'unacceptable'

The attack on a UN-run school in Gaza by the Israeli military was "totally unacceptable and totally indefensible", the US has said.

White House spokesman Josh Earnest told reporters that Israel has to "do more" to protect civilians.

He was referring to an incident on Wednesday, when at least 16 people were killed when shellfire hit a UN-run school designated as a civilian shelter in the Jabaliya district of Gaza City.

Israeli spokesman Mark Regev told the BBC earlier that Israel would apologise if it discovered it was responsible.