The U.N.'s atomic watchdog and other experts say radiological contamination is likely inside a key uranium enrichment site at Natanz that was badly damaged by Israel and then hit by U.S. strikes early Sunday.

The move, the first time the U.S. has attacked Iran, is a major escalation of the conflict between Israel and Iran.

Iran’s most heavily fortified nuclear site is at Fordo, a hilly area south of Tehran and about 15 miles away from Qum, a city where more than a million people live.