Reuters quoted unnamed Palestinian militants and Israeli intelligence sources as saying that Awad al-Qiq, 33, acting headmaster at the UNRWA-run Rafah Boys' Preparatory School was by night secretly a rocket builder for Islamic Jihad.

A handwritten note outside the school posted on the metal gate at the entrance to the school declared that the teacher, killed in an air strike last week, was "the chief leader of the engineering unit", who would now find "paradise".

Christopher Gunness, a spokesman for the UN Relief and Works Agency, which employs more than 9,000 local staff in Gaza, said that the agency was regularly instructed not to engage in political or militant activities of any kind. It has summarily sacked employees found to be in breach of the instruction.

Mr Gunness added: "We have a zero-tolerance policy towards politics and militant activities in our schools. Obviously, we ... cannot police people's minds." Family members and a student at the school said they had no idea that the dead man, a physics teacher with eight years' experience teaching at UN schools, was involved in militant activities.

UNRWA also announced that it now had enough fuel to distribute food aid for 20 days to the 700,000 refugees who need it. Earlier, the agency had warned that the shortage of fuel would mean it would have to halt food aid from last night.

Petrol operators in Gaza, who had refused to go on distributing supplies, which had been severely limited because of the Israeli-imposed blockade, said last week that they had emptied fuel tanks on the Palestinian side of the Nahal Oz crossing, allowing Israel to refill them.