The medical system in Gaza is close to being overwhelmed and the Palestinian enclave faces a humanitarian catastrophe if a cease fire is not reached soon, a senior UN health official said Friday, a day after a Gaza City hospital was seriously damaged by Israeli shelling. Sixteen health facilities, including hospitals and primary health care clinics, have been damaged by shelling and fighting since Israel unleashed its military offensive against Gaza on Dec. 27, said Tony Laurance, the head of the UN World Health Organization's office in Gaza. The attacks are a “grave violation of international humanitarian law,” Laurance said in a telephone interview. “If this continues it will be a humanitarian catastrophe, especially for the health care system.” On Friday, health workers were sifting through the charred and still smoldering five-story Al-Quds hospital, which is operated by the Palestinian Red Crescent Society. There was nothing left to salvage inside the blackened hulk, which had been hit by three shells. “They shelled the building, the hospital building. It caught fire. We tried to evacuate the sick people and the injured and the people who were there. Fire fighters arrived and put out the fire, which burst into flames again and they put it out again and it came back for the third time,” paramedic Ahmad Al-Haz told Associated Press Television News as he stood Friday outside the building. Khaled Abu Zeid, a medic reached by phone at the hospital Thursday, that the attack set the hospital's pharmacy ablaze and that about 400 patients and staff were briefly trapped inside the main hospital building. Laurance said most of the patients were transferred to Gaza's City's already crowded Al-Shifa hospital. In Geneva, the Red Cross movement condemned the shelling of the hospital. The damage caused was “completely and utterly unacceptable based on every known standard of international humanitarian law,” the International Federation of Red Cross and Red Crescent Societies said in a statement. Nearly 1,100 Palestinians have been killed during the Israeli offensive, aimed at forcing Hamas to halt its rocket fire on southern Israel. Of the dead, 346 were children and 79 women, according to the United Nations. More than 4,900 Palestinians have been injured. Thirteen Israelis have been killed and more than 70 wounded. “These latest attacks on hospitals in Gaza are an outrage and have put at risk the lives of patients and staff and prevented access to health care for a system that is already coping with a flood of seriously wounded people,” Laurance said. “We have had recent assurances that health personnel working in the field would not be attacked. What happened in Gaza overnight was unacceptable.” He said 13 medical workers have been killed and 22 wounded during the war, adding that 16 ambulances were also destroyed. “Emergency rooms, intensive care wards are already at maximum capacity. In terms of beds we are almost there,” he said. Gaza's health system will face a long-term burden, he warned. “We have an extensive number of serious injuries, amputations and head injuries that will have serious long-term repercussions,” he said. Laurance said that Gaza did not need additional doctors or medicines as the international “response has been overwhelming.” What WHO needed, he said, were funds.