BEIRUT — Palestinians in northern Gaza described heavy Israeli bombardment Saturday in the hours after airstrikes killed at least 22 people, as Israel continued to tell people there and in southern Lebanon to get out of the way of its offensives against the Hamas and Hezbollah militant groups. In Lebanon, the United Nations peacekeeping force said its headquarters in Naqoura had again been hit, with a peacekeeper struck by gunfire late Friday and in stable condition.