The crisis sparked in the Middle East a week ago by the barrage of US and Israeli strikes on Iran "has been spreading like wildfire", Volker Turk told reporters in Geneva.

"The world urgently needs to see steps to contain and extinguish this blaze," he said, lamenting that "instead, we are only seeing more inflammatory, bellicose rhetoric, more bombings, more destruction, killings, and escalation that fuels it further".

"I urge the states involved to take immediate steps to de-escalate, to give peace a chance. And on other states to call clearly on those involved to pull back," he said.

"Cool heads must prevail if we are to prevent further terror and devastation for civilians."

His comments came as fresh strikes rocked Iran and Lebanon on Friday, with Israel vowing to escalate to a new phase in the Middle East war that has spiralled rapidly throughout the region and beyond.

The war has dragged in global powers, upended the world's energy and transport sectors, and brought chaos to even usually peaceful areas of the volatile region.

Turk voiced particular concern about the situation in Lebanon, which he said was "becoming a key flashpoint".

"I am extremely concerned and worried about the latest developments following Hezbollah's attacks on Israel and Israel's heavy counter-strikes, as well as its extensive displacement orders that have already forced hundreds of thousands of people to flee their homes," he said.

"I call for an immediate cessation of hostilities."

The UN rights chief lamented that "confusion has also been sown around international law", and that "some have openly derided the fundamental values of our common humanity".

"Given the magnitude of this crisis, I call on heads of state and government around the world unequivocally to commit to defending international human rights law, international humanitarian law and the UN Charter itself," he said.

"We cannot afford for more powder kegs to ignite."