Total siege of Gaza 'prohibited' under international law: UN

Volker Turk, the UN high commissioner for human rights, said people's dignity and lives had to be respected as he called for all sides to defuse the "explosive powder-keg situation".

Palestinian militant group 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, and sparking fears of an increasingly desperate humanitarian situation.

"International humanitarian law is clear: the obligation to take constant care to spare the civilian population and civilian objects remains applicable throughout the attacks," Turk said in a statement.

The siege risk seriously compounding the already dire human rights and humanitarian situation in Gaza, including the capacity of medical facilities to operate, especially in light of increasing numbers of injured, the statement said.

"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.

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, the statement added.