Vice-President Joe Biden has said that the United States would not stand in the way if Israel chose to attack Iran’s nuclear facilities, even as he reiterated an offer to Tehran for negotiations over its nuclear programme.

In an interview on ABC television, Mr Biden said the US could not interfere with any sovereign decision that Israel might take to defend itself against an Iranian nuclear threat.

“Look, Israel can determine for itself — it’s a sovereign nation — what’s in their interest and what they decide to do relative to Iran and anyone else," Mr Biden said. “We cannot dictate to another sovereign nation what they can and cannot do.”

Mr Biden’s remarks came even as the top military official in the US warned of the “unintended consequences” of a strike against Iranian nuclear sites.

Israel has made little secret of its desire to deal with Iran militarily, although senior military officials there admit that they probably lack the capacity to guarantee success.

White House officials denied that Mr Biden’s remarks marked a toughening in Washington’s attitude to Tehran in the wake of the Iranian Government’s hardline stance against protests against the disputed elections.

They may indicate, though, how Washington is striving to keep ahead of the quickly changing situation in Tehran after its offer of re-engagement. Mike Mullen, chairman of the Joint Chiefs of Staff, said that the military option could not be taken off the table even as the Administration pursued engagement.

By appearing to support Israeli military action, Mr Biden may be hoping to apply indirect pressure on Iran without having to issue any such threat himself, keeping diplomatic channels clear. Washington is aware that Israel would be unable to launch any strike without its co-operation to secure airspace rights over Iraq.

Israel’s hawkish Foreign Minister, Avigdor Lieberman, welcomed Mr Biden’s comments today praising them as “very logical”. Although the two allies sometimes have disagreements over the wisdom of Israeli military action, he noted, “at the end of the day the decision is ours”.

Israelis, however, are keenly aware of what the short-term consequences of a strike on Iran could mean for its own security, despite the widespread belief that a nuclear armed Iran would pose an existential threat.

The chairman of the Iranian parliament’s National Security and Foreign Policy Committee, Alaeddin Boroujerdi, warned that Iran would respond to any attack by Israel. “If it occurred, then the Islamic Republic of Iran will respond in a very full-scale and very decisive way,” he said.

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