The heads of 15 United Nations aid organizations and private groups called for an immediate end to the fighting in the Gaza Strip in a joint statement on Friday, warning that the entire population of northern Gaza is at risk of death. They said the situation in the north of the coastal strip, where Israel’s army launched a new ground offensive against the Islamist organization Hamas at the beginning of October, is particularly dramatic. “The entire Palestinian population in North Gaza is at imminent risk of dying from disease, famine and violence,” said the statement, published by the UN Inter…