Pentagon officials fear that Israel may attack Iran's nuclear facilities before the end of this year, which would have enormous security and economic repercussions for the United States and the rest of the world, media reports said on Tuesday.

"There is an increasing likelihood that Israel will carry out such an attack, a move that would prompt Iranian retaliation against, not just Israel, but against the United States as well," a senior Pentagon official was quoted as saying by the ABC television network.

The widely held view among Pentagon officials, it said, is that an Israeli attack would do only temporary damage to Iran's nuclear programme but it would cause major problems in the region and beyond, prompting a wave of attacks on US interests in Iraq, the Persian Gulf and elsewhere.

The official, ABC News said, have identified two 'red lines' that could trigger an Israeli offensive.

The first is, when Iran's Natanz nuclear facility produces enough highly enriched uranium to make a nuclear weapon.

According to the latest US and Israeli intelligence assessments, that is likely to happen sometime in 2009, and could happen by the end of this year, it added.

"The red line is not when they get to that point, but before they get to that point," the official was quoted as saying. "We are in the window of vulnerability."

The second red line is connected to when Iran acquires the SA-20 air defence system it is buying from Russia [Images]. The Israelis may want to strike before that system -- which would make an attack much more difficult -- is put in place, the report said.

Some Pentagon officials, the network said, were also worried that Israel may be determined to attack before a new US president, who may be less supportive, is sworn in January next year.

Pentagon officials, ABC News said, believe the massive Israeli air force exercise in early June, first reported by the New York Times, was done to prepare for a possible attack.

A senior official called it 'not a rehearsal, but basic, fundamental training', required to launch an operation against Iran.

"The Israeli air force has already conducted the basic exercise necessary to tell their senior leadership, 'We have the fundamentals down.' Might they need some more training and rehearsals? Yes. But have they done the fundamentals? I think that is what we saw," the official told ABC News, adding that if Israel moves closer to military action, he expects to see more exercises like the one conducted in early June.

The chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, was in Israel over the weekend for a series of meetings with senior Israeli military officials, including, Lieutenant General Gabi Ashkenazi, the chief of staff of the Israeli Defence Forces, ABC News said.

According to a military spokesman, Iran's nuclear programme was a major topic of discussion.