More detail: Trump has said for days that Iran should make a nuclear deal with the U.S. But his message became more dire as he warned the Iranian capital's roughly 10 million residents to flee in the dead of night.

"Giving up entirely," Trump told reporters early on Tuesday. "Iran cannot have a nuclear weapon, it's very simple." The air war between Iran and U.S. ally Israel - which began on Friday when Israel attacked Iran with airstrikes - has raised alarms in a region that had already been on edge since the start of Israel's military assault on Gaza in October 2023.

President Donald Trump in about eight hours went from suggesting a nuclear deal remained “achievable” to urging Tehran’s 9.5 million residents to flee for their lives