US fears Israel may be preparing to strike Iran

Israel is preparing a military strike against Iran over US objections, triggering Americans to step up contingency plans to safeguard its facilities in the region in case of a conflict.

President Barack Obama, defence Secretary Leon Panetta and other top US officials have delivered a string of private messages to Israeli leaders, warning about dire consequences of a strike, Wall Street Journal reported quoting Pentagon sources.

Obama spoke on phone on Thursday with Israeli Prime Minister Benzamin Netanyahu and Gen Martin Dempsey, chairman of the joint chiefs of staff is rushing to Tel Aviv to top meet top Israeli military officials.

"Our concern is heightened," a senior US military official said of the probability of an Israeli strike over US objections.

Tehran crossed at least one of Israel's "red lines" earlier this month when it announced it had begun enriching uranium at the Fordow underground nuclear facility near the holy city of Qom.

The planned closing of Israel's nuclear plant near Dimona this month, which was reported in Israeli media, sounded alarms in Washington, where officials feared it meant Israel was repositioning its own nuclear assets to safeguard them against a potential Iranian counterstrike.

The high-stakes planning and diplomacy comes as US officials warn Tehran, including through what administration officials described yesterday as direct messages to Iran's leaders, against provocative actions.

Tehran has warned that it could retaliate to tightened sanctions by blocking oil trade through the Strait of Hormuz.

On Thursday, Iran's Supreme Leader Ayatollah Ali Khamenei vowed to punish the perpetrators of the assassination—blamed by Iran on the US and Israel—of an Iranian scientist involved in the nuclear programme.

The US denied the charge and condemned the attack. Israel hasn't commented.

Covert efforts by Israel's intelligence service to prevent Tehran from developing nuclear weapons have been credited with slowing the programme without the high risk of military conflict that could be sparked by an airstrike. Iran says its nuclear programme is for peaceful uses.

But Israel has declined to rule out a strike, as has the US.

"It is the policy of the Israeli government, and the Obama administration, that all options remain on the table. And it is crucial that the ayatollahs in Tehran take this policy seriously," said Michael Oren, Israel's ambassador to the US.

The US military is preparing for a number of possible responses to an Israeli strike, including assaults by pro-Iranian Shiite militias in Iraq against the US Embassy in Baghdad, according to US officials.

The US believes its embassy and other diplomatic outposts in Iraq are more vulnerable following the withdrawal of US forces last month. Up to 15,000 US diplomats, federal employees and contractors are expected to remain in Iraq.

In large measure to deter Iran, the U.S. has 15,000 troops in Kuwait, and has moved a second aircraft carrier strike group to the Persian Gulf area.

It has also been pre-positioning aircraft and other military equipment, officials say. Arms transfers to key allies in the Gulf, including the United Arab Emirates and Saudi Arabia, have been fast-tracked as a further deterrent, officials say.