The operation raised urgent questions about what remained of Tehran's nuclear program and how its weakened military might respond. The price of oil rose as financial markets reacted.
Iran lashed out at the U.S. for crossing "a very big red line" with its risky gambit to strike the three sites with missiles and 30,000-pound bunker-buster bombs.
President Donald Trump, who has warned of additional strikes if Tehran retaliates against U.S. forces, has mused about the possibility of "regime change in Iran, despite administration officials earlier indicating they wanted to restart talks with Iran. U.S. Secretary of State Marco Rubio, in an interview with CBS, said: "Let's meet directly."
Ali Akbar Velayati, an adviser to Iran's supreme leader, said any country used by the U.S. to strike Iran "will be a legitimate target for our armed forces," the state-run IRNA news agency reported.
Tens of thousands of American troops are based in the Middle East.