Only the convincing threat of military action headed by the United States will persuade Iran to drop plans to build an atomic bomb, Prime Minister Benjamin Netanyahu said on Tuesday.

Speaking to foreign journalists, he said that although the latest round of international sanctions were hurting Iran, they would not be enough to force a u-turn on nuclear weapons.

"You have to ratchet up the pressure and ... I don't think that this pressure will be sufficient to have this regime change course without a credible military option that is put before them by the international community led by the United States," he said.

The West believes that Iran aims to use its uranium enrichment program to build atomic weapons. Tehran denies this.

Both Israel and the United States have said all options remain on the table, but many analysts believe the threat of military intervention has receded amid signs that Iran's contested nuclear program is suffering from sabotage, sanctions and technical glitches.

Israel's outgoing spy chief told reporters last week that he did not believe Iran would be able to build a nuclear bomb before 2015 and counseled against any pre-emptive military strikes.

A political source said Netanyahu was very unhappy with the departing Mossad director Meir Dagan for airing his views in public and the prime minister shrugged off his comments on Tuesday.

"I think that intelligence estimates are exactly that, they are estimates. They range from best case to worst case possibilities ... so I think there is room for some differing assessments," he said.

He told reporters the world had finally realized the danger posed by a nuclear-armed Iran and praised the latest round of United Nations-led sanctions for taking its toll on Tehran.

"There is no question that all these things have caused hardship but they have not in any way altered Iran's determination to pursue its nuclear program. They are determined to move ahead despite every difficulty, every obstacle, every setback, to create nuclear weapons."

Netanyahu also bemoaned the influence Iran exerted on the whole Middle East, suggesting it was a potential impediment to any peace deal between Israel and its northern neighbor, Syria.

"There is a very strong relationship between Syria and Iran and I don't see any clear willingness on the part of Syria to break that relationship. That is another consideration whether things can actually move forward," he said.