The Israel Defence Force has initiated a four-hour ceasefire for humanitarian relief in Gaza, which began at 3pm local time.

Lt Col Peter Lerner, a spokesman for the IDF warned that if Hamas did not respect the truce, things “are going to get messier”.

But the militant group said that Israel’s unilateral decision to call for a halt in the fighting was a media stunt, arguing it only applied to certain areas where military operations were not ongoing.

The move comes as the UN sharply criticised Israel for the shelling of another UN school in the Jabaliya refugee camp, killing 15 and wounding 125 others.

A spokesman for the UN Relief and Works agency said the “world stands disgraced” by the Israeli military The UN said the attack represented “a source of universal shame”.

The last humanitarian ceasefire declared by Israel was on July 27, and lasted for 24 hours. Hamas, however, did not honour the truce and continued to send rockets into Israeli territory throughout the period, prompting the IDF to return fire.

UPDATE: Early reports say that during the ceasefire a further 15 have been killed and 160 wounded in an Israeli air strike which hit a market in the Gaza City neighbourhood of Shejaiya.

Three Israeli soldiers also lost their lives during recent operations in the southern Gaza Strip, bringing the IDF death toll to 56.