US and Israeli threats of a military strike have done nothing to stop Iran's pursuit of a nuclear capability, Israeli Prime Minister Benjamin Netanyahu said on Wednesday in talks with US Defence Secretary Leon Panetta.

"You yourself said a few months ago that when all else fails, America will act. But these declarations have also not yet convinced the Iranians to stop their programme," Netanyahu told the Pentagon chief.

"This must change, and it must change quickly because time to resolve this issue peacefully is running out."

Panetta issued his own warning to Iran over its efforts to develop what Israel and much of the West believe is a bid for military nuclear capability.

"They have a choice to make," he told reporters on a visit to an Iron Dome missile defence battery in the southern port town of Ashkelon with Israeli Defence Minister Ehud Barak.

"They can either negotiate in a way that tries to resolve these issues and has them abiding by international rules and requirements and giving up their effort to develop their nuclear capability.

"But if they don't, and if they continue to make the decision to proceed with a nuclear weapon ... we have options that we are prepared to implement to ensure that does not happen."

Israel, the sole if undeclared nuclear power in the Middle East, has repeatedly warned that a nuclear Iran would pose an existential threat to it, and both Israeli and US officials have repeatedly warned that all options -- including a military strike -- were on the table for preventing such a scenario.

"You recently said that sanctions on Iran are having a big impact on the Iranian economy, and that is correct," Netanyahu told Panetta. "But unfortunately it is also true that neither sanctions nor diplomacy have yet had any impact on Iran's nuclear weapons programme.

And until now, Iran had not taken seriously US or Israeli threats of a military strike on its uranium enrichment facilities, he said.

"However forceful our statements, they have not convinced Iran that we are serious about stopping them," said Netanyahu who has repeatedly warned that a military action may be necessary.

On Tuesday, the Israeli leader said he had not yet decided whether to mount a military strike on Iran's enrichment facilities.

But he also said Israel would not rely on anyone else to guarantee its security -- not even Washington.

Panetta reiterated US pleas for more time to let diplomacy and sanctions work before considering a strike.

"We have to exhaust every option, every effort before we resort to military action," he said in Ashkelon.

"It is my responsibility as secretary of defence to provide the president with a full range of options, including military options should diplomacy fail," he added.

Asked how the Obama administration would react in the event of a unilateral Israeli strike, Panetta said that the question of what was in Israel's national security interest "is something that must be left up to the Israelis."

Barak said it was extremely unlikely that sanctions and diplomacy would convince Iran to abandon its nuclear ambitions, which Tehran insists are peaceful.

"The probability of this happening is extremely low," he remarked, noting that Iran was pushing ahead with daily enrichment of "uranium needed for their weapon."

"We have clearly have something to lose by this stretched time," he remarked.

Speaking ahead of his arrival in Israel, Panetta ruled out talks on "potential attack plans" with the Israelis.

"I think it's the wrong characterisation to say that we're going to be discussing potential attack plans," he said in Cairo. "What we are discussing are various contingencies on how we would respond."

Washington, he said, was continuing to "work on a number of options in that area." He did not give further details.

Panetta also met on Wednesday in Jerusalem with Israeli President Shimon Peres who said Iran is "the only country that is both imperialist and threatening to destroy another country."

"It is not just a theoretical wish, it is supported by terror, by intervention in the affairs of other countries and the development of a nuclear bomb," Peres's office quoted him as telling his guest. "We cannot live in a world with imperial ambition and nuclear weapons and no laws, no limitations, no respect."