"Attacking Iran would be insane," ElBaradei, the director general of the International Atomic Energy Agency, told Der Spiegel in an interview to appear Monday.
"This would trigger an explosion across the whole region and the Iranians would immediately start to construct a (nuclear) bomb and would be assured the support of the entire Muslim world," he said.
The comments from ElBaradei, who is due to step down as IAEA chief in November, come amid public radio reports that leaders of the new Israeli government had given undertakings to that effect to Central Intelligence Agency chief Leon Panetta during a secret visit two weeks ago.
Hawkish Prime Minister Benjamin Netanyahu took a strong line on Iran's nuclear programme during the campaign for February's parliamentary election and has described the Islamic republic as an "existential threat" to the Jewish state.
But Deputy Foreign Minister Danny Ayalon said Saturday that Israel would not launch an attack without advance approval from the United States.
"We need the Americans as much from a logistic point of view as for our own defence on the international level after any such strike," the Y-Net news website quoted him as saying.
Israel, widely considered to be the Middle East's sole if undeclared nuclear power, accuses Iran of seeking to develop nuclear weapons. Tehran says its nuclear programme is purely to produce energy for a rapidly growing population once fossil fuels run out.
Israel considers the Islamic Republic to be its main enemy due to numerous statements by President Mahmoud Ahmadinejad that the Jewish state should be "wiped off the map."
