Israel's armed forces chief-of-staff does not believe Iran will take the decision to build a nuclear bomb, he told an Israeli newspaper in an interview published on Wednesday.

Speaking to the left-leaning Haaretz newspaper, Lieutenant General Benny Gantz said Iran was going "step-by-step to the place where it will be able to decide if it wants to manufacture a nuclear bomb.

"It still hasn't decided yet whether to go the extra mile," he was quoted as saying, expressing a view also held by the administration of US President Barack Obama.

As long as its nuclear facilities were unprotected from attack, "the programme is too vulnerable from (Iran's) perspective," Gantz said.

Iran has already developed the capacity to enrich uranium to 20 percent, which is used to create medical isotopes, but going "the extra mile" would mean working to enrich to 90 percent -- the level needed to make nuclear weapons.

"If the supreme religious leader Ayatollah Ali Khamenei wants, he will move forward towards acquiring a nuclear bomb, but along the way, a decision must still be taken," he said.

"It will be taken if Khamenei believes he is immune from a response.

"In my opinion, he would be making a huge mistake if he does so, and I don't think he will want to go the extra mile," Gantz said.

"I think that the Iranian leadership is made up of very rational people."

Gantz said 2012 would be a very important year, but he was reluctant to describe it as make-or-break.

"Clearly, the more the Iranians progress the worse the situation is. This is a critical year, but not necessarily 'go, no-go.'

"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."

He also said the growing campaign of diplomatic pressure and international sanctions imposed on Iran was beginning to work.

"The pressure is starting to bear fruit," he said.

"I also expect that someone is building operational tools of some sort, just in case. The military option is the last chronologically but the first in terms of its credibility," he explained.

"If it's not credible it has no meaning. We are preparing for it in a credible manner."

His language in discussing Iran were far from the fiery rhetoric used by Israeli Prime Minister Benjamin Netanyahu, Haaretz said.

Last week, Netanyahu said anyone who refused to acknowledge the Iranian threat had learned nothing from the Nazi Holocaust during World War II.

"They are afraid to speak the truth, which is today, as it was then, that there are people who want to annihilate millions of Jews."

Israel and much of the West suspect Iran is using its civilian nuclear programme as a cover for a weapons drive -- a charge which Tehran vehemently denies.

In recent months, there have been growing concerns the Jewish state might launch a pre-emptive military strike on Iran in a bid to destroy, or at least severely disable, its nuclear programme.