The comments followed a closely held meeting at the Pentagon Monday between Israeli Defense Minister Ehud Barak and US Defense Secretary Robert Gates.

"I think the Israelis are keenly aware that we believe the best possible avenue of dissuading the Iranians from pursuing nuclear weapons is through economic and political pressures," said Geoff Morrell, the Pentagon press secretary.

"We certainly understand that the Israelis view a nuclear Iran as an existential threat -- they have made that abundantly clear to us, to the world. And we are working diligently to prevent that from happening," he said.

"But the way we are focusing our efforts is on diplomatic, economic, financial pressures," he said.

Morrell added that "a military option is always available to us. It's not our first choice."

The Israeli defense ministry, meanwhile, said Barak had urged Gates to keep all options open.

"A policy that consists of keeping all options on the table must be maintained," it quoted Barak as saying.

"Iran's plans pose a threat to regional and global stability. We insist that it is vital to continue tightening the economic and financial sanctions imposed on the Iranians," he said.

The United States and Israel are both convinced that Iran's nuclear program is aimed at acquiring nuclear weapons. Iran insists that it is for civilian energy purposes only and has defied international sanctions against it.

Despite the difference in emphasis, Morrell said the two sides had a "shared strategic vision and a common understanding of the threats to the Middle East and emanating from it."

Gates assured Barak that they would explore providing Israel with additional defensive capabilities, Morrell said.

The Pentagon press secretary declined to confirm an Israeli statement that the capabilities included a forward deployed missile defense radar, missile early warning launch data, and counter-measures against short-range rockets and mortars.

Morrell said the Barak-Gates meeting was kept small on purpose to keep details from getting out.

Gates was accompanied by Admiral Michael Mullen, the chairman of the Joint Chiefs of Staff, and Eric Edelman, the undersecretary of defense for policy. Barak was with the Israeli ambassador to Washington and a general, Morrell said.

The meeting came amid a continuing diplomatic impasse with Iran over its nuclear drive and just days after Tehran announced that its uranium enrichment facility in Natanz has now expanded to 6,000 centrifuges.

It also came after the United States on July 19 took the unprecedented step of sending a top diplomat to meet Iran's chief negotiator at talks in Geneva aimed at resolving the standoff.

Washington also indicated it was considering sending diplomatic personnel to Tehran to open a US interests section there.

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