The U.N. nuclear watchdog has no indication Israeli and U.S. attacks on Iran have hit any nuclear facilities, its chief Rafael Grossi told the agency's Board of Governors on Monday, moments before Iran's envoy said one was targeted a day earlier.

Iran's nuclear program has been among the reasons Israel and the U.S. have given for the attacks, alleging Iran was getting too close to being able to eventually make an atom bomb.

At the same time, what remains of Iran's atomic facilities after the two militaries attacked them in June appears to have been largely spared in this campaign so far.

"We have no indication that any of the nuclear installations ... have been damaged or hit," International Atomic Energy Agency chief Rafael Grossi said in a statement to a meeting of his agency's 35-nation Board of Governors.

What that assessment was based on is unclear, since he also said his agency had not been able to reach its counterparts in Iran. Tehran has not let the IAEA return to its bombed facilities since they were attacked in June.

"Efforts to contact the Iranian nuclear regulatory authorities ... continue, with no response so far. We hope this indispensable channel of communication can be re-established as soon as possible," he said.

Moments later, Iran's ambassador to the IAEA, Reza Najafi, told reporters outside the closed-door meeting that the sprawling nuclear complex at Natanz had been attacked.

Natanz housed two uranium-enrichment plants that were attacked in June - an above-ground one that the IAEA says was destroyed and an underground one that was at least badly damaged, among other facilities.

"Again they attacked Iran's peaceful, safeguarded nuclear facilities yesterday," Najafi said. Asked by Reuters which facilities were hit, he replied: "Natanz" and left.