United Nations, Oct 12 : UN Secretary-General Antonio Guterres has warned against the spillover of the ongoing Israeli-Palestinian conflict. "We must avoid spillover of the conflict. I am concerned about the recent exchange of fire along the Blue Line (between Israel and Lebanon) and recent reported attacks from southern Lebanon," he told a press briefing on Wednesday, Xinhua news agency reported. "I appeal to all parties -- and those who have an influence over those parties -- to avoid any further escalation and spillover," the UN chief said. Guterres called for the immediate release of all Israeli hostages held in Gaza. Civilians must be protected at all times. International humanitarian law must be respected and upheld, he added. About 220,000 Palestinians are now sheltering in 92 facilities run by the UN Agency for Palestine Refugees across Gaza. UN premises and all hospitals, schools and clinics must never be targeted, Guterres said. Crucial life-saving supplies, including fuel, food and water, must be allowed into Gaza. There is a need for rapid and unimpeded humanitarian access, he said. Guterres thanked Egypt for its "constructive engagement" to facilitate humanitarian access through Rafah, the sole crossing point between Egypt and the Gaza Strip, and to make the El Arish airport available for critical assistance. Israel has imposed a "complete siege" of Gaza following Hamas attacks on Israel over the weekend. /IANS