UN nuclear watchdog chief Rafael Grossi said on Wednesday his top priority is getting his inspectors back to Iran's nuclear facilities to assess the impact of US and Israeli military strikes and verify its stocks of enriched uranium.

"This is the number 1 priority," International Atomic Energy Agency chief Grossi told a news conference at an Austrian security cabinet meeting. He is seeking his inspectors' return to Iranian sites including the three plants where it was enriching uranium until Israel launched strikes on June 13.

Asked if Iran had informed him of the status of its stocks of enriched uranium, particularly its uranium enriched to up to 60% purity, close to weapons grade, he pointed to a letter he received from Iran on June 13, saying Iran would take "special measures" to protect its nuclear materials and equipment.

"They did not get into details as to what that meant but clearly that was the implicit meaning of that. We can imagine this material is there," Grossi said, suggesting much of that material had survived the attacks.