Israel told the United Nations that the entire population of the northern Gaza Strip, about 1.1 million people, should move south within the Palestinian territory in 24 hours — an order that a U.N. spokesman said would be impossible “without devastating humanitarian consequences.” Hamas described the Israeli warning as psychological warfare and urged people not to comply. The Israeli military said all residents of Gaza City should move south from their homes “for their own safety,” as Israeli strikes pummel the densely populated enclave. The United Nations said more than 420,000 people are already displaced in Gaza, where residents are facing power shortages and hospital supplies are dwindling under siege. Israel has been massing forces for an anticipated ground incursion since Hamas militants staged one of the deadliest attacks in Israeli history.