Worshippers trample on a portrait of US President Barack Obama during the funeral of nuclear scientist Mostafa Ahmadi-Roshan, who was killed in a bomb attack in Tehran this week while left, Obama speaks from the White House on Friday. The White House has warned Iran that any attempts to cut off oil supplies from the gulf will be resisted. Pictures: REUTERS

The Obama administration said on Friday it is warning Iran through public and private channels against any action that threatens the flow of oil from the Persian Gulf.

Spokesmen were vague on what the US would do about Iran’s threat to block the strategic Strait of Hormuz, but military officials have been clear that the US is readying for a possible naval clash.

That prospect is the latest flashpoint with Iran, and one of the most serious.

Although it currently overshadows the threat of war over Iran’s disputed nuclear programme, perhaps beginning with an Israeli military strike on Iran’s nuclear structure, both simmering crises raise the possibility of a shooting war this year.

“We have to make sure we are ready for any situation and have all options on the table,” Defence Secretary Leon Panetta said, addressing a soldier’s question this week about the overall risk of war with Iran.

The US still hopes that international pressure will persuade Iran to back down on its disputed nuclear programme, but the Islamic regime shows no sign that it would willingly give up a project that has become a point of national pride.

A bomb, or the ability to quickly make one, could also be worth much more to Iran as a bargaining chip down the road.

Time is short, with Iran making several leaps towards the ability to manufacture a weapon if it should choose to do so. Iran says its nuclear development is intended for the peaceful production of nuclear energy.

Meanwhile, several longstanding assumptions about US influence and the value of a targeted strike to stymie Iran’s progress towards a nuclear weapon have changed.

For one, the White House is no longer confident it could prevail on Israel not to launch such a strike.

An escalating covert campaign of sabotage and targeted assassinations, highlighted by this week’s killing of an Iranian nuclear scientist, may not be enough to head off a larger shooting war, and could prod Iran to strike first.

The brazen killing of a young scientist by motorcycle-riding bombers is almost surely the work of Israel, according to US and other officials speaking on condition of anonymity. The killing on a Tehran street followed the deaths of several other Iranians involved in the nuclear programme, a mysterious explosion at an Iranian nuclear site that may have been sabotage and the apparent targeting of the programme with an efficient computer virus.

Iranian officials accuse both Israel and the US of carrying out the assassination as part of a secret operation to stop Iran’s nuclear programme.

The killing came a day after Israeli military chief Lieutenant General Benny Gantz was quoted as telling a parliamentary panel that 2012 would be a “critical year” for Iran, in part because of “things that happen to it unnaturally”.

Israel considers Iran its mortal enemy and takes seriously the Iranian threat to wipe the Jewish state from the map. The US is Israel’s strongest ally and international defender, but the allies differ over how imminent the Iranian threat has become, and how to stop it.

The Obama administration worries that Iran’s claim this week that it is expanding nuclear operations with more advanced equipment, may push Israel closer to a strike.

A senior commander of the Revolutionary Guard force was recently quoted as saying that Tehran’s leaders had decided to order the closure of the Strait of Hormuz if the country’s petroleum exports are blocked due to sanctions.

Panetta linked the two crises on Thursday, saying an Iranian nuclear weapon is one “red line” the US will not allow Iran to cross, and a closure of the strait another.

“We must keep all capabilities ready in the event those lines are crossed,” Panetta told troops in Texas.

International talks to barter Iran out of building a nuclear weapon have nearly collapsed, the US and several partners are on the verge of applying the toughest sanctions yet on Iran’s lifeblood oil sector, an increasingly cornered Iranian leadership is lashing out in unpredictable ways and faces additional internal pressures with a parliamentary election approaching. All that adds up to a new equation, US and Western diplomats said.

A unilateral US military strike on Iran’s nuclear infrastructure remains unlikely but no longer unthinkable, while the likelihood of an Israeli military strike has increased.

Immediate consequences probably would include an unpredictable spike in oil prices, ripple effects in troubled European economies and a setback for the fragile US economic recovery.

Longer term, a strike or full-on war would almost surely ignite anti-American sentiment in the Middle East and beyond, and empower hard-line political movements in newly-democratic Egypt and elsewhere. – Sapa-AP