Gaza City (Palestinian Territories) (AFP) - A United Nations school sheltering displaced Palestinians in central Gaza came under Israeli fire on Tuesday as a team was inspecting damage from a day earlier, a UN official said.

The official said a team, with Israeli clearance, was at the school run by the UN agency for Palestinian refugees UNRWA in Al-Maghazi when Israeli tank shelling resumed, hitting the building on Tuesday afternoon.

"Yesterday we got reports that it was shelled and so today we sent our guys down to investigate and see which side the fire came from," the official said, speaking to AFP on condition of anonymity.

"They went down there with Israeli clearance, and while they were there, they came under Israeli shelling," he added.

He said that there were holes blown through the walls of the school compound and that the gates had been blown off but no one was injured in the shelling.

The school has been evacuated and UNRWA has submitted a formal letter about the shelling to Israel, he added.

UNRWA is sheltering more than 100,000 people at more than 60 of its schools throughout the Gaza Strip.

Many Palestinians living in border areas of Gaza have been warned by Israel to flee their homes, but they say they feel nowhere in the coastal enclave is safe for them.

On Thursday, UNRWA said it was investigating after finding 20 rockets hidden in one of its vacant schools.

It condemned the incident as a "flagrant violation" of international law and said the rockets had been removed and the "relative parties" informed.

It said the incident was the first of its kind.