A diplomatic effort to evacuate U.S. citizens from Gaza faltered after Egyptian officials said they would only allow foreigners to cross the border if aid could pass in the opposite direction. Egypt’s refusal on Saturday, confirmed by three officials and in an announcement on state television, thwarted the latest U.S. push to evacuate any of the 500 or more Americans in Gaza wishing to leave through the enclave’s southern border with Egypt. Israel—which has sealed off Gaza’s northern border with a ground invasion by Israeli forces believed imminent—said Saturday that it would give a few hours of safe passage for...