An attack by Israel on Iran's nuclear facilities could trigger a month-long conflict on multiple fronts that could cost hundreds of Israeli lives, the outgoing civil defence chief has said.

Matan Vilnai, who will step down from his position to become Israel's ambassador to China, outlined the bloody scenario in an interview with Israel's Maariv daily.

"There is no room for hysteria. Israel's home front is prepared as never before," he said.

His comments came as part of a rising chorus of reports that Israel was gearing up to attack Iran's nuclear facilities. The most recent report claimed that Jerusalem could attack before November's presidential elections in the United States.

US defence secretary Leon Panetta has tried to quash rumours of an assault by saying that Washington did not believe Israel had made a decision.

"I don't want to be dragged into the debate," Vilnai said. "But the United States is our greatest friend and we will always have to coordinate such moves with it."

Vilnai warned that Israelis should be ready for a brutal retaliation with hundreds of missiles targeting cities on a daily basis and leading to the deaths of 500 people.

"There might be fewer dead, or more, perhaps but this is the scenario for which we are preparing, in accordance with the best expert advice," Vilnai said.

Missiles striking the home front

"The assessments are for a war that will last 30 days on several fronts," he said, alluding to the possibility an Iranian-Hezbollah-Palestinian coordinated response.

"Just as the citizens of Japan have to understand they are likely to be hit by an earthquake, Israelis must realise that anyone who lives here has to be prepared for missiles striking the home front," Vilnai said.

Although Israeli officials have refused to rule out the possibility of an Israeli-led attack on Iran, they have said a military strike was likely to trigger a violent response both directly and indirectly by Iran.

The conflict would in turn increase tensions on both the Israel-Lebanon front and Gaza-Israel front.

Analysts have also warned an attack could trigger a global terror campaign against Israel and a spike in oil prices.

Vilnai will leave office by the end of August and will be replaced by Avraham Dichter, a previous head of the Shin Bet, Israel's domestic intelligence agency.