Palestinians are "facing a precipice" in Gaza, the top UN refugee official there told the Security Council on Thursday in a strongly-worded appeal for action. With more than 220,000 Palestinians already sheltering in UN facilities -- four times the number from the last Gaza conflict in 2008-2009 -- Philippe Krahenbuhl said he had reached breaking point. "We have exceeded the tolerable limit that we can accommodate," Krahenbuhl said, adding that he was "alarmed" by the latest Israeli instructions to civilians to evacuate two areas in Gaza targeted for more attacks. Krahenbuhl spoke to the Council by audiolink from Gaza after Israel vowed to press on with its military campaign to destroy a network of tunnels used by Hamas militants for attacks.