Israel's military chief, Benny Gantz, has stated he doesn't believe Iran will decide to make nuclear weapons and that Iranian key decision makers are rational.

Speaking to the Israeli daily, Haaretz, Gantz said: "[Iran] is going step by step to the place where it will be able to decide whether to manufacture a nuclear bomb. It hasn't yet decided whether to go the extra mile."

The chief of staff of the Israel Defence Forces said the decision to develop nuclear weapons is only in the hands of the supreme leader, Ayatollah Ali Khamenei.

"If the supreme religious leader Ayatollah Ali Khamenei wants, he will advance it to the acquisition of a nuclear bomb, but the decision must first be taken. It will happen if Khamenei judges that he is invulnerable to a [military] response," he said in the interview published on Wednesday.

"I believe he would be making an enormous mistake, and I don't think he will want to go the extra mile."

"I think the Iranian leadership is composed of very rational people. But I agree that such a capability, in the hands of Islamic fundamentalists who at particular moments could make different calculations, is dangerous."

According to Gantz, western pressure on Iran by means of diplomacy and economic sanctions has had an effect on Tehran's rulers but a military response is still an option, albeit the last.

He said 2012 is a critical year for Iran but not necessarily a year of "go, no-go". "The problem doesn't necessarily stop on 31 December 2012. We're in a period when something must happen: Either Iran takes its nuclear programme to a civilian footing only or the world, perhaps we too, will have to do something. We're closer to the end of the discussions than the middle."

"If Iran goes nuclear it will have negative dimensions for the world, for the region, for the freedom of action Iran will permit itself," he said.

Gantz's comments are at odds with those recently expressed by the Israeli prime minister, Benjamin Netanyahu, who warned in a CNN interview in Jerusalem on Tuesday that sanctions "better work soon".

"[The sanctions] are certainly taking a bite out of the Iranian economy … [But] they haven't rolled back the Iranian program – or even stopped it – by one iota," he told the CNN.

This month, Iran and world's major power resumed nuclear talks in Istanbul after 15 months of break in negotiations. Both sides expressed optimism after Istanbul talks and agreed to meet for a second round of negotiations in Baghdad late May.

Excessive focus on Iran's nuclear programme by the international community has been criticised by an Iranian activist who believes it will cast a shadow on violations of human rights in the country. Iran's Nobel Peace prize laureate, Shirin Ebadi, pressed western politicians this week not to forget human rights and democracy in their talks with Tehran leaders.