The International Committee of the Red Cross has accused the Israeli military of "unacceptable" conduct and breaching international humanitarian law after discovering four emaciated children living next to the corpses of their mothers and other adults in bomb-shattered houses in Gaza City.

The ICRC said that it had spent four days seeking Israeli guarantees of safe passage so that it could gain access to the houses in the badly damaged Zaytun neighbourhood of the city. It was finally allowed to send in a rescue team and four Palestine Red Crescent Society ambulances yesterday afternoon and said today that what they found was shocking.

In one house they discovered four small children, alive but too weak to stand, next to the bodies of their dead mothers. In all their were 12 dead bodies lying on mattresses.

In another house they found 15 survivors of the Israeli bombardment, several of them wounded, and in a third, three corpses. At that point they were ordered to leave by Israeli soldiers manning a post some 80 metres away, but they refused to do so.

The children and the wounded had to be taken to the ambulances by donkey cart because earth walls erected by the Israeli army made it impossible to bring the vehicles close enough to the houses. In all, the rescue team removed 18 wounded and 12 others who were extremely exhausted. It took away two corpses and plans to return to fetch 13 more tomorrow.

The ICRC said that it believed there were more wounded sheltering in the ruins of other houses in the same neighbourhood, and in an unusually robust public statement issued by the organisation's Geneva headquarters it demanded that the Israeli military grant it immediate access to search for them.

"This is a shocking incident," Pierre Wettach, the ICRC's head of delegation for Israel and the Occupied Palestinian Territories, said. "The Israeli military must have been aware of the situation but did not assist the wounded. Neither did they make it possible for us or the Palestine Red Crescent to assist the wounded."

The ICRC accused the Israeli military of failing to meet its obligation under international humanitarian law to care for and remove the wounded, and called the delay in allowing rescue services access unacceptable.

The ICRC's charges were another setback for the Israeli military. On Tuesday it killed more than 40 people in a bomb attack on a UN school in the Gaza Strip that it claimed was being used by a Hamas mortar team, and international aid organisations say that its 13-day offensive is creating a humanitarian catastrophe among Gaza's 1.5 million residents.

The Israel Defence Forces did not respond directly to the charges, but issued a statement that it was battling a terrorist organisation — Hamas — that was deliberately using Palestinian civilians as human shields.

It said the IDF was working closely with international aid organisations during the fighting so that civilians could receive assistance, and continued: "The IDF in no way intentionally targets civilians and has demonstrated its willingness to abort operations to save civilian lives and to risk injury in order to assist innocent civilians.

Any serious allegations made against the IDF's conduct will need to be investigated properly, once such a complaint is received formally, within the constraints of the current military operation."

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