U.S. Secretary of State Marco Rubio rushed to assure the world that America had not been involved after Israel launched overnight strikes on Iranian nuclear facilities. But, almost instantly, Iran made clear it wasn’t buying it—and warned that Washington would be held accountable too.

The country was not building a nuclear weapon, the national intelligence director told lawmakers, and its supreme leader had not reauthorized the dormant program.

Israel's air campaign on the Iranian capital appeared to broaden on the fourth day of an intensifying conflict after it issued warnings on Monday for about 300,000 people in Tehran to evacuate ahead o...