The U.S. was preparing to launch a retaliatory strike against Iran for shooting down an American reconnaissance drone Thursday, but the mission was called off at the last minute, U.S. officials said.

Details about the mission or the reason for the abrupt reversal of plans weren’t immediately known, but officials said a future military response hasn’t been ruled out.

The U.S. appeared to be edging closer to military confrontation throughout the day on Thursday as President Trump charged that Tehran had made “a very big mistake” in shooting down the unmanned drone.

But as the hours went by, each side refrained from additional escalatory steps, and Mr. Trump later appeared to defuse the crisis by suggesting that the shootdown might have been done without the blessing of Tehran’s top leadership.

“I imagine someone made a mistake,” Mr. Trump told reporters. “We didn’t have a man or woman in the drone. It would have made a big, big difference.”