JERUSALEM  — Kicking off his election campaign, Israeli opposition leader Shaul Mofaz on Thursday accused Prime Minister Benjamin Netanyahu of being driven by an obsession to bomb Iran.

Mofaz, head of the centrist Kadima party that quit Netanyahu's coalition weeks ago citing differences over how to rein in Iran's nuclear program, unveiled a poster of a flaming mushroom cloud emblazoned with "Netanyahu will mire us in trouble."

A former defense chief, Mofaz is launching a vigorous bid to win votes, with opinion polls predicting Kadima tumbling from parliament's largest faction to holding as few as four seats after the election on January 22.

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Convening a news conference at Kadima headquarters near Tel Aviv, Mofaz branded a union forged this week between Netanyahu's right-wing Likud party and Foreign Minister Avigdor Lieberman's hardline faction as "very dangerous for Israel's future."

Using language that echoed warnings months ago by another of Israel's former security chiefs, Mofaz said Netanyahu and Lieberman were driven by "a Messianic belief to bomb Iran."

"Netanyahu is leading us on a Messianic path, toward a collision, in an irresponsible and irrational way," Mofaz said.

"We mustn't let Netanyahu carry out this obsession," he added, urging Netanyahu's defeat, though pollsters see the government easily winning re-election in January.

Netanyahu sees a mortal threat to Israel in the prospect of an Iranian nuclear bomb.

But some of Israel's national security figures have come out against the possibility of Netanyahu launching a preemptive war, saying this may backfire by alienating Israel's main ally the United States and driving Iran — which denies seeking nuclear weapons — to take the final steps to their production.