"This is just the latest atrocity to befall the people of Gaza where the fighting has entered an even more terrifying phase, with increasingly dreadful humanitarian consequences," Martin Griffiths, the UN humanitarian chief, said in a statement.

He said "The world seems unable, or unwilling, to act," adding "This cannot go on. We need a step change."

On Tuesday, an Israeli airstrike on a residential complex at the Jabalia refugee camp in the north of the Gaza Strip killed at least 50 people and injured tens.

Hamas said seven captives, including three foreign passport holders, had died in the bombing.

Palestinian rescuers reported fresh strikes on the camp on Wednesday.

Griffiths, the UN Under-Secretary-General for Humanitarian Affairs, released his statement after a two-day visit to the region.

The death toll among Palestinians has reached 8,800 people, including 3,600 children and 2,290 women, and the number of wounded climbed over 22,000.

More than half of the 2.3 million Palestinians have been internally displaced after Israeli airstrikes destroyed more than 40 percent of all residential units in the strip.

The UN and humanitarian organizations have called on Israel to lift its near-month-old food-water-fuel blockade on the strip, as thousands of Palestinians teeter on the edge of starvation.

The Palestinian health ministry in Gaza has said that more than 1,000 dead children lie under the rubble