Israel rebuffed as "unworthy" on Sunday comments by the U.N. nuclear watchdog chief that any Israeli or U.S. attack on Iran's nuclear facilities would be illegal.

Having visited Tehran in a bid to loosen deadlocked talks on renewing its 2015 nuclear deal with world powers, International Atomic Energy Agency chairman Raphael Grossi on Saturday said "any military attack on nuclear facilities is outlawed."

He was responding to a reporter's question about threats by Israel and the United States to attack Iran's nuclear facilities if they deem diplomacy meant to deny it the bomb to be at a dead end. Tehran says its nuclear program is peaceful.

"Rafael Grossi is a worthy person who made an unworthy remark," Israeli Prime Minister Benjamin Netanyahu told his cabinet in televised remarks on Sunday.

"Outside what law? Is it permissible for Iran, which openly calls for our destruction, to organize the tools of slaughter for our destruction? Are we forbidden from defending ourselves? We are obviously permitted to do this."

The IAEA said on Saturday Grossi had received sweeping assurances from Iran that it will assist a long-stalled investigation into uranium particles found at undeclared sites and re-install removed monitoring equipment.