by Anne Davies and Jason Koutsoukis

Israeli officials have welcomed comments by US Vice-President Joe Biden that America would not stand in the way of an Israeli strike against Iranian nuclear plants.

Mr Biden contradicted his country's most senior military commander, Admiral Mike Mullen, when he responded, three times, to questions on the American ABC's This Week program that Israel was free to do what it needed to do.

"If the Netanyahu Government decides to take a course of action different than the one being pursued now, that is their sovereign right to do that. That is not our choice," Mr Biden said.

Israeli officials have read the comments as a sign the US is preparing a "plan B" in the event that its proposed dialogue with Iran fails to rein in Tehran's uranium enrichment program.

Speaking in Tokyo, Alaeddin Broujerdi, the head of Iran's parliamentary committee on national security and foreign policy, said Iran was ready to take decisive action if Israel attacked its nuclear operations.

"Both the US and Israel are aware of the consequence of an erroneous decision," Mr Broujerdi said. "I believe our response will be real and decisive."

President Barack Obama told Israeli Prime Minister Benjamin Netanyahu in May that he expected to know by the end of the year whether Iran was making "a good-faith effort to resolve differences" in ending its nuclear program, signalling that his willingness to engage in diplomacy over the issue had limits.

Israel reportedly gave serious thought to a pre-emptive strike against Iran's Natanz nuclear complex last year but was told by then US president George Bush that the US would not support such a move.

Officials in Jerusalem were not surprised by Mr Biden's comments, saying that while the Obama Administration might not have given the green light to an Israeli attack against Iran, it was not withholding approval.

"There are secret understandings between Israel and the Obama Administration as to the options that Israel has regarding Iran," said one political source quoted by the newspaper Israel Today.

The newspaper quoted sources in Mr Netanyahu's office as saying that "the fact that Biden is talking about Israel's right to attack Iran, and at the same time fewer statements are being made on settlements, shows that Mr Netanyahu is succeeding, slowly and determinedly, in persuading the Americans of the justice of his Government's policy".

The liberal Israeli daily Haaretz said Israel now believed the US was considering more punitive action against Iran, such as tighter sanctions, but still wanted to give dialogue a chance of succeeding.

Mr Biden's comments appeared at odds with those of Joint Chiefs of Staff chairman Admiral Mullen, who seemed to warn against an Israeli strike on Iran in appearances on CBS' Face the Nation and Fox News Sunday. "I worry about it being very destabilising, not just in and of itself, but the unintended consequences of a strike like that," Admiral Mullen told CBS.