The head of the team, John Ging, said the extent of the destruction was appalling.

BBC: Russians flee Syrian conflict on planes from Beirut

Infrastructure repairs were being made, but 400, 000 people still had no water, according to Ging.

CNN: Palestinians: 1,300 killed, 22,000 buildings destroyed in Gaza

Mr Ging said humanitarian organisations were deeply frustrated as they were ready to deploy with large stocks of food and medicine.

BBC: Humanitarian crisis in Sudan south gets worse, says UN

"Some areas are reduced to rubble so we have to find a temporary solution for them and also get the reconstruction operation under way, " said Mr Ging.

BBC: Agencies rush aid to Gaza Strip

Also on Tuesday, an artillery shell struck inside a second U.N. school in the same town, but the boys' prep school was empty at the time, UNRWA director John Ging said.

CNN: U.N. agency demands Israel support claims about militants at school

John Ging, director of operations in Gaza for the UN relief agency Unrwa, told the BBC that delivering water was the first priority, and he called on Israel to open its border crossings with the enclave.

BBC: Agencies rush aid to Gaza Strip

John Ging, head of the U.N.

CNN: Rice calls on Israel to avoid crisis