Israel-Palestine conflict: Total siege of Gaza 'prohibited' under international law, says UN

Israel's total siege of the Gaza Strip, depriving civilians of goods essential for survival, is banned under international law, the United Nations human rights chief said on Tuesday.

Volker Turk called for all sides instead to defuse the "explosive powder-keg situation", as Israel warned of a sustained war to destroy the Palestinian militant group Hamas.

"We know from bitter experience that vengeance is not the answer, and ultimately innocent civilians pay the price," Turk said.

Hamas, which abducted about 150 people in its surprise weekend assault on Israel, threatened to execute the hostages if Israeli air strikes continue "targeting" Gaza residents without warning.

The threat came after Israel on Monday imposed a total siege on the Gaza Strip, cutting off food, water and electricity supplies.

"The imposition of sieges that endanger the lives of civilians by depriving them of goods essential for their survival is prohibited under international humanitarian law," Turk said in a statement.

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The siege risks seriously compounding the already dire human rights and humanitarian situation in Gaza, the statement said.

Any restrictions on the movement of people and goods to implement a siege must be justified by military necessity or may otherwise amount to collective punishment, it added.

Turk called on influential countries to try to de-escalate the situation.

"We know how this plays out, time and time again -- the loss of Israeli and Palestinian lives and incalculable suffering inflicted on both communities," he said.

The UN high commissioner for human rights said he was "deeply shocked and appalled by allegations of summary executions of civilians, and, in some instances, horrifying mass killings by members of Palestinian armed groups".

"It is horrific and deeply distressing to see images of those captured by Palestinian armed groups being ill-treated, as well as reports of killings and the desecration of their bodies," he added.

"Civilians must never be used as bargaining chips."