Israel said on Friday it had surrounded the Gaza Strip's biggest city, while mounting casualties among Palestinian civilians have intensified calls by global leaders for a ceasefire.

Calls for a pause in the conflict comes as the territory also faces acute shortages of food, water, medicine and fuel.

Gaza health authorities say at least 9,061 people have been killed in Gaza since Israel launched its assault on the enclave of 2.3 million people in retaliation for deadly attacks by Hamas militants on southern Israel on October 7.

A group of independent United Nations experts warned Palestinians there are at "grave risk of genocide".

"We call on Israel and its allies to agree to an immediate ceasefire. We are running out of time," the group of UN special rapporteurs said in a statement.

Israel has dismissed calls for a ceasefire, claiming it targets Hamas fighters whom it accuses of intentionally hiding among the population and civilian buildings. The White House has also rejected calls for a ceasefire.

Meanwhile, US Secretary of State Antony Blinken was due to visit Israel for the second time in a month to meet Prime Minister Benjamin Netanyahu.

As Blinken left Washington for the Middle East, he said he would discuss concrete steps to minimise harm to civilians in Gaza.

The White House has said any pauses in fighting should be temporary and localised, and insisted they would not stop Israel defending itself. (Reuters)