Shaul Mofaz, Israel's transportation minister, has officially launched his campaign to replace Ehud Olmert, the Israeli prime minister, as leader of the Kadima party.

One of the frontrunners for Olmert's job, Mofaz denounced his native Iran as "the root of all evil", in a radio interview on Tuesday, a day after his official campaign for the party leadership began.

In an interview on Israel radio he urged Western powers to impose stiffer sanctions on Tehran to pressure Iran to stop a nuclear programme that he said would pose "a threat to Israel's existence".

Opinion polls show that while Mofaz, who is a deputy prime minister, is highly ranked in the contest to lead the Kadima party, he trails Tzipi Livni, the foreign minister.

Olmert, who is currently under investigation for corruption, said last week he would step down once a successor for the party leadership has been chosen.

The party leadership election is to take place next month.

While he supports diplomacy to resolve the standoff with Tehran, Mofaz said in June that an Israeli attack to halt Iran's nuclear project may be "unavoidable" unless a deal was reached.

Iran says its nuclear development is for civilian purposes only, to produce energy.

Israel is widely believed to have assembled the Middle East's only nuclear arsenal which experts say comprises as many as 200 warheads.

Israel does not discuss its nuclear capabilities under a so-called "strategic ambiguity" policy.