Israel's outgoing home front defence minister says an attack on Iran would likely trigger a month-long conflict that would leave 500 Israelis dead.
Matan Vilnai told the Maariv newspaper that the fighting would be "on several fronts", with hundreds of missiles fired at Israeli towns and cities.
Israel was prepared, he said, though strikes on Iran's nuclear facilities had to be co-ordinated with the US.
Meanwhile, a US blogger has published what he says are Israel's attack plans.
Richard Silverstein told the BBC he had been given an internal briefing memo for Israel's eight-member security cabinet, which outlined what the Israeli military would do to prevent Iran developing nuclear weapons.
Analysis
By Jonathan Marcus
BBC Diplomatic Correspondent
The text of the purported Israeli cabinet memo is just that, text. There is no document as such and thus it is impossible to verify if it is indeed an Israeli cabinet paper of some kind. But its purpose for Richard Silverstein is clear. He believes it was passed by a serving officer to the politician and then leaked by him precisely to alert the outside world to the scale of Israel's military plan to strike at Iran and thus to reduce the chances of it ever happening.
An unprecedented public debate is under way in Israel on the wisdom of launching an attack against Iran. And this leaked document, whatever its source, and whatever its original purpose, has become an element in that debate.
The document itself is striking in both the scale and scope of the military operation that it proposes. It also employs a range of technologies, many of which we have known that the Israelis are developing, but this document suggests that they are battle-ready and fully operational.
Leaked memo: propaganda or war plan?
Tehran insists its nuclear programme is entirely peaceful.
