President Biden spoke Friday morning to the families of 14 Americans who remain unaccounted for in Israel after Hamas militants staged one of the deadliest attacks in Israeli history over the weekend. The call was “gut-wrenching,” Biden said at a news conference, adding that “we’re not going to stop until we bring them home.” Hours earlier, Israel called on the entire population of the northern Gaza Strip — about 1.1 million people — to move south within 24 hours. Israeli strikes are pounding the densely populated Palestinian territory, and troops are massing nearby ahead of an anticipated ground incursion. Hamas described the evacuation warning as psychological warfare and urged people not to comply. Authorities in Gaza said there was nowhere safe to go while under siege, and health officials said it would be impossible to evacuate hospitals, which are facing power shortages and dwindling supplies.