The United States has a military option "ready" if diplomacy fails to halt Iran's controversial nuclear programme, the US envoy to Israel has said, an Israeli newspaper reported on Thursday.

"It would be preferable to resolve this diplomatically through the use of pressure than to use military force," right-wing nationalist daily Makor Rishon quoted Daniel Shapiro as telling an Israeli bar association meeting this week.

"But that doesn't mean that option is not fully available," the newspaper quoted him as saying. "It is not just available, but it is ready; the necessary planning has been done to ensure that it is ready."

In Washington, State Department spokeswoman Victoria Nuland said Shapiro was completely in sync with White House policy.

"Ambassador Shapiro's comments were designed to reflect completely what the president has said all along, which is that even as we move forward with the P5+1 discussions with Iran and hope that we can settle these issues through diplomacy that we nonetheless take no option off the table," she said.

The United States, Israel and much of the international community believe Iran's nuclear programme masks a weapons drive, a charge Tehran denies.

Washington has pursued a policy of pushing tough sanctions against Iran, while leaving the door open to a diplomatic resolution.

After a 15-month hiatus, Iran and the P5+1 powers -- Britain, China, France, Russia and the United States plus Germany -- met in Istanbul in mid-April, in talks described as "positive."

They are to meet again in Baghdad on Wednesday.

Israel has expressed scepticism about the talks, warning they could simply give Tehran more time to pursue a weapon.

Israeli Defence Minister Ehud Barak said on Monday that the demands being made of Tehran "are so minimalist that even if Iran were to accept all of them, it could still continue and advance its nuclear programme."

Barak met Thursday with US Defence Secretary Leon Panetta for their third session of talks in the Pentagon in as many months and thanked him for Washington's pledge of $70 million (55 million euros) in funding for more batteries of Israel's Iron Dome anti-missile system.

"The additional aid for acquiring Iron Dome batteries is being given at a most important time," Barak's office quoted him as saying. "Iron Dome batteries allow us, the political leadership, more diplomatic room for manoeuvre and will help avoid escalation."

The statement said the meeting lasted for about an hour and covered "all the regional issues."

The announcement fell short of predictions in Israeli media that Washington was ready to commit to $680 million (530 million euros) to pay for more anti-rocket batteries over several years.

Instead, the US administration chose to provide $70 million for the current year and review the issue in future years, allowing some potential leverage over Israel.

Three Iron Dome batteries deployed in southern Israel performed successfully against rocket fire by Gaza militants in March, and Barak has said he intends to deploy more throughout the country.

The system was developed by Israel with the help of US funding.

The United States spent $204 million (159 million euros) on the Iron Dome system in 2011.

"Defence ties between Israel and the US have never been stronger," Barak said.

Israel has publicly warned it is keeping all options, including a military strike, on the table when it comes to dealing with the Iranian nuclear programme.

Its stance on the issue has led to speculation that it could carry out unilateral military action, despite the caution of US officials who have repeatedly stressed that sanctions must be given a chance to work.