An assessment of the costs and benefits of attacking Iran says U.S. military strikes probably would trigger Iranian retaliation that carried risks of igniting all-out war in the Middle East.
The report by former government officials, national security experts and retired military officers says U.S. attacks would shake the Iranian regime's political control and damage its ability to launch counterstrikes.
But it says the Iranians probably would manage to retaliate, directly and through surrogates.
The assessment is to be released publicly on Thursday. An advance copy was provided to The Associated Press.
The report says achieving more than a temporary setback to Iran's nuclear program would require a military operation -- including a land occupation -- more taxing than the Iraq and Afghanistan wars combined.