Volker Turk said, "extremely serious allegations of multiple and profound breaches of international humanitarian law, whoever commits them, demand rigorous investigation and full accountability".

Turk was speaking after a visit last week to the Middle East, where he warned that both sides were committing war crimes in the deadly conflict.

"Where national authorities prove unwilling or unable to carry out such investigations, and where there are contested narratives on particularly significant incidents, international investigation is called for," he said in a briefing to UN member states in Geneva.

Turk was unable to go to Israel or the Palestinian territories despite having requested access.

Turk said the crisis was extending well beyond the Gaza Strip, voicing deep concern about the "intensification of violence and severe discrimination against Palestinians in the occupied West Bank, including East Jerusalem".

"In my view, this creates a potentially explosive situation and I want to be clear: we are well beyond the level of early warning. I am ringing the loudest possible alarm bell about the occupied West Bank," he said.

Turk said his most important recommendation was that all parties had to acknowledge that all human lives have equal value.

"It is apparent that on both sides, some view the killing of civilians as either acceptable collateral damage, or a deliberate and useful weapon of war. This is a humanitarian and human rights catastrophe," he said.

"We must not let rage submerge our moral compass. We must not lose our grip on reality to the myth that pain can be eradicated by unleashing it on a scapegoat."

He added: "Israelis' freedom is inextricably bound up with Palestinians' freedom. Palestinians and Israelis are each others' only hope for peace."