At least 29 Palestinian civilians were unlawfully killed by missile-firing Israeli drones during its offensive in the Gaza Strip, a US human rights group said.

A report by Human Rights Watch, published six months after the operation, said that Israel had failed to exercise proper caution “as required by the laws of war” in their use of drones. Mrac Galasco, a senior military analyst for Human Rights Watch, said that although 29 cases had been highlighted in the report, as many as 87 civilians could have been killed in drone attacks.

"It is absolutely unacceptable, clearly unlawful, and not what we expect from the world's most moral military," he said.

Israel heavily relies on a fleet of drones — unmanned aerial vehicles — to patrol the Gaza Strip. Their technology is among the most sophisticated in the world, Mr Garlasco said, so it was all the more surprising that so many civilians could have been targeted.

"They used as much force as they could use at any time… It seems clear that there was something of a shoot first and ask questions later.”

In one case, also examined by The Times, a missile hit the rooftop of the al-Habbash family in Gaza City. Of the six children playing on the roof, two were killed instantly, while two others lost their legs.

Muhammad Amr al-Habbash, 16, the oldest of the children and the only to survive intact, said that he had heard a buzz overhead before feeling himself blown backwards by the force of the blast.

“I felt the pressure throw me back, and then my cousins were gone in front of me,” he said

Independent analysts say that that it would be difficult to prove that the missile which struck the rooftop was fired from a drone. But Mr Garlasco said that he had examined shrapnel on the scene, including small fragments of tungsten, and had “no doubts” that the missile was fired by a drone.

Israel has refused to comment on the specific cases in the report or to release video footage of the attacks.

A number of organisations have published reports questioning Israel’s tactics during the three-week offensive, including the use of white phosphorous and other munitions. Earlier this week, the UN began holding public hearings in Gaza City and Geneva into allegations that war crimes were perpetrated during the operation.

Israel is not a party to the International Criminal Court and has refused to co-operate with the UN mission — led by a South African judge, Richard Goldstone — making it unlikely that the charges will be brought to trial.

The Israeli military has refuted the criticism, stating that their behaviour “conformed to international law, as do all weapons and munitions used.”

A military spokesman faulted the group for relying on the testimony of Palestinian witnesses "whose knowledge of military issues is doubtful".

Israel launched its operation to try to halt rocket attacks from the Hamas-controlled Gaza Strip. At least 1,400 Palestinians and 13 Israelis were killed during the offensive.

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