Nearly 55 million tonnes of debris must be cleared across Gaza before reconstruction can begin, a United Nations Development Programme (UNDP) official said on Thursday, during a visit to the enclave.

"This is equal to 13 Pyramids of Giza, just to give you an indication of the challenge that will be required," said Jaco Cilliers, special representative for the UNDP Programme of Assistance to the Palestinian People.

Two years of Israeli bombardment have left vast parts of Gaza in ruins; about 83 percent of all buildings have been damaged, according to the United Nations Satellite Centre.