"The war games were unsuccessful at preventing the conflict from escalating," an unnamed Air Force source told the magazine in its latest issue.

The Central Intelligence and the Defense Intelligence Agency played out the possible results US strikes, the magazine reported.

Hawks within President George W. Bush's administration haev advocated for regime change in Tehran -- through covert operations or force if needed, Newsweek said.

But with US-led forces facing almost daily attacks in Iraq, no one in Bush's cabinet has taken up the cause, the report said.

The United States believes Iran is using a civlian nuclear program to mask a weapons development effort.

Iran insists its nuclear programme is strictly aimed at generating electricity, despite suspicions it is seeking to develop the capability to build nuclear weapons.

Uranium is enriched through centrifuges to make what can be fuel for civilian nuclear reactors but also the explosive material for atomic bombs.

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