Mossad chief travelled to Washington to gauge US reaction to Iran strike

The highly sensitive content of Mr Pardo's discussion with his American counterparts has been revealed in a Newsweek article entitled 'Obama's Dangerous Game With Iran'.

Unnamed US officials claim the Israeli security chief's line of questioning to CIA chief David Petraeus ran: "What is our posture on Iran? Are we ready to bomb? Would we [do so later]? What does it mean if [Israel] does it anyway?"

Mr Petraeus told a Senate Select Committee in a public hearing broadcast live on US television last month that he had met with Mr Pardo to discuss Israel's growing concern over Iran's nuclear aspirations.

When asked in the same briefing if Israel intends to strike, James Clapper, director of US national intelligence, told the committee chair that he would prefer to answer her question behind closed doors.

US sources quoted in the Newsweek report added that Israel has refused to share with the US a "significant" amount of intelligence regarding its military preparations.

Israeli officials refused to respond to the article on Monday, which goes on to question how much influence the US president has over Israel and how far the Obama administration will be willing to go to prevent Iran's nuclear armament.

According to Yehuda Ben Meir, a former Israeli deputy minister of foreign affairs and expert on Israel-US relations, full US backing is by no means a prerequisite for an Israeli strike.

"It's a matter of degrees of grey – will the US apply strong pressure on Israel to hold off on attack or will it say, 'we don't think this is the right time to act but it's your decision'. The outcome depends on a very nuanced exchange at the highest possible level," Mr Ben Meir said.

"The situation is developing day by day. More and more, the US position is going out on a limb and making it clear that it sees a nuclear Iran as an unacceptable danger to the world and if they decide to, they can prevent it."

Washington has so far held a clear line on the issue of Iran, asking for time and space for sanctions to work. But while the Iranian economy has suffered a major dint as a result of combined US and EU economic isolation, news that India has emerged as the largest customer of Iranian oil, flouting an international trade embargo, will undoubtedly lessen the crippling effect of sanctions that the US is hoping for.

On Monday, Vice Admiral Mark, who leads the US naval fleet in the Gulf, added muscle to Washington's repeated assertions that it has not ruled out a military solution to the Iranian nuclear threat should sanctions fail.

Speaking from the US military base in Bahrain, Vice Admiral Fox assured journalists that his fleet is capable of preventing Iran from blocking the Strait of Hormuz, even while Iran is boosting its naval capabilities in the Gulf with mines and boats prepared for suicide attacks.

The Islamic straight has threatened to block the international waterway if economic sanctions shut down its oil trade or its nuclear facilities come under attack.

"They have increased the number of submarines ... they increased the number of fast attack craft. Some of the small boats have been outfitted with a large warhead that could be used as a suicide explosive device. The Iranians have a large mine inventory," he said.

"We've developed very precise and lethal weapons that are very effective, and we're prepared. We're just ready for any contingency."