Ehud Olmert told Germany's Bild Zeitung on Saturday: "[Mahmoud] Ahmadinejad speaks today like Hitler before taking power. He speaks of the complete destruction and annihilation of the Jewish people."
The Iranian president has expressed doubts over whether the Jewish Holocaust took place and called for Israel to be "wiped off the map".
He has also suggested the Jewish state should be moved to Europe or North America.
"So you see, we are dealing with a psychopath of the worst kind, with an anti-Semite," Olmert said. "God forbid that this man ever gets his hands on nuclear weapons, to carry out his threats."
Iran says it has the sovereign right to enrich uranium to use as fuel in power stations.
Israel, believed to have the Middle East's only atomic arsenal, says Iran is months away from acquiring the know-how to make nuclear weapons. Other experts say Iran is still years away from being able to produce a nuclear weapon.
Mohamed ElBaradei, head of the UN International Atomic Energy Agency (IAEA), delivered a report on Friday saying UN checks in Iran had been hampered and Tehran had rebuffed requests to stop making nuclear fuel.
The Islamic Republic said on Saturday it was willing to resume allowing snap UN atomic inspections if its case were dropped by the UN Security Council and passed back to the IAEA.