U.N. Secretary-General Ban Ki-moon is “deeply concerned” by the resurgence of factional violence in Gaza, which has resulted in at least 20 deaths, U.N. spokeswoman Michele Montas said Tuesday. “The intensity of this latest round of fighting and the heightened public rhetoric marks a serious deterioration of the situation, placing the civilian population in Gaza in grave peril, jeopardizing the delivery of humanitarian assistance, and threatening the future of the Palestinian government and authority,” Montas told reporters. Ban called for an immediate cessation of all violence and asked that all parties to give full support to Palestinian President Mahmoud Abbas to restore law and order. Hamas and Fatah loyalists battled for a sixth consecutive day in the Gaza Strip on Tuesday. The violence has put humanitarian assistance from the U.N. Relief and Works Agency (UNRWA) in jeopardy. “Three of UNRWA's five food-distribution centers and seven of UNRWA's 18 health clinics were forced to close as fighting raged in their immediate vicinity and in some cases spilled over into the premises today,” according to the U.N. agency for Palestinian refugees. “Eighty percent of the refugee population is totally aid dependent; the economy has collapsed under the weight of the international economic embargo, leaving Palestinian refugees in unprecedented misery and despair,” UNRWA said.