BAGHDAD (AP) — After more than three years of combat operations, Iraq announced Saturday that the fight against the Islamic State group is over after the country's security forces drove the extremists from all of the territory they once held. Iraqi and American officials warned, however, that key challenges remain despite the military victory.

Prime Minister Haider al-Abadi formally announced the victory in an address to the nation aired on Iraqi state television Saturday evening.

"Honorable Iraqis, your land has been completely liberated," he said. "The liberation dream has become a reality....