A classified US war simulation held to assess potential fallout from an Israeli attack on Iran predicts it would spark a broader regional war involving the United States, The New York Times reported Tuesday.
The simulation was not considered a rehearsal, the report said, but does indicate potential risks from such an attack.
"The results of the war game were particularly troubling to General James Mattis, who commands all American forces in the Middle East, Persian Gulf and Southwest Asia," the report said, citing unnamed officials familiar with the effort.
"When the exercise had concluded earlier this month, according to the officials, General Mattis told aides that an Israeli first strike would be likely to have dire consequences across the region and for United States forces there," it added.
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The two-week simulation, dubbed Internal Look, highlighted a series of potential events in which "the United States found it was pulled into the conflict" after Iranian missiles struck a US Navy warship in the Gulf, killing about 200 Americans, according to officials with knowledge of the exercise.
The simulation indicated US forces would retaliate by carrying out its own strikes on Iranian nuclear facilities, the report said.
The Islamic republic has been buffeted in recent months by ramped-up Western economic sanctions.
It has also been threatened with possible military action against its nuclear facilities by Israel and the United States.
Throughout, Tehran has maintained that its nuclear program is purely peaceful, denying Western suspicions -- largely echoed in a November report by the International Atomic Energy Agency -- that it was conducting military research towards designing nuclear weapons.