Stephen Sackur speaks to Philippe Lazzarini, head of UNRWA, the UN\u2019s refugee agency for Palestinians. This week, six UN relief agency staff were killed in an Israeli strike on a central Gaza school that had been turned into an emergency shelter for thousands. UNRWA\u2019s death count in Gaza since the beginning of the war is over 220. Is his agency\u2019s mission now impossible?