There is no power, water or fuel in Gaza, and food is running dangerously low, Griffiths said, urging all countries with influence to use it to ensure respect for the rules of war, and avoid further escalation.

The actions and rhetoric by Hamas militants and Israel in the past few days is "extremely alarming, unacceptable," Griffiths said.

Civilians and civilian infrastructure must protected, he said.

In Gaza, families have been bombed while inching their way south along congested, damaged roads, following an evacuation order by Israel that left hundreds of thousands of people scrambling for safety but with nowhere to go, Griffiths said.

Even wars have rules, and these rules must be upheld, at all times, and by all sides, he said.

"Civilians must be allowed to leave for safer areas. And whether they move or stay, constant care must be taken to spare them," Griffiths said.

He said anyone held captive must be treated humanely and all hostages must be released.

"Civilians in Israel and the Occupied Palestinian Territory are suffering from a week of utter anguish and devastation," Griffiths said. "I fear that the worst is yet to come."

"The past week has been a test for humanity," he said, "and humanity is failing."