A central United Nations compound in the Gaza Strip has been hit by white phosphorus shells in the fighting between Hamas and the Israeli military Thursday, UN officials said, according to DPA. Several hundred Palestinians were estimated to be inside the building. The attack drew sharp condemnation from UN Secretary-General Ban Ki-moon, who was in Tel Aviv talking with Israeli officials on a ceasefire for the enclave. "I conveyed my strong protest and outrage to the defence minister and the foreign minister and demanded a full investigation," said Ban, adding that "Defence Minister Barak said to me it was a grave mistake." The central warehouse in the compound was ablaze and fuel supplies were not safe from the fire, officials said. The compound houses large fuel reserves to allow humanitarian agencies to carry out their work. "White phosphorus cannot be put out with water, but we do not have any sand in the compound," said Chris Gunness, a spokesman for UNRWA, the aid agency for Palestinian refugees. The building was clearly marked with UN flags. The UN has suspended all work in the area. Some 700 Palestinians were seeking refuge inside the compound when it was hit, and the UN has been unable to evacuate them, with one official adding that "there is no where safe to go." Adnan Abu Hasna, also with UNRWA, denied there was any militant activity inside the compound, which serves as the headquarters for several key UN groups.