The 22 Arab countries at the United Nations joined in demanding an immediate ceasefire in Gaza after hundreds of people were killed in an explosion at a Gaza City hospital that Hamas attributed to an Israeli airstrike but the Israeli military said was caused by a misfired militant rocket. Riyad Mansour, the Palestinian UN ambassador, said Arab Group members are “outraged by this massacre” and also united in demanding the immediate delivery of humanitarian aid and preventing “forcible displacement” of Palestinians.