The report by the Oxford Research Group said on Monday that any bombing of Iran by US forces, or by their Israeli allies, would have to be part of a surprise attack that would inevitably catch many Iranians unprotected and could eventually lead to a lengthy confrontation involving many other countries in the region.
An attack could lead to the closure of the Gulf at the Straits of Hormuz and would probably have a substantial impact on oil prices, as well as spurring new attacks by Muslim radicals on Western interests, the report said.
"A US military attack on Iranian nuclear infrastructure would be the start of a protracted military confrontation that would probably involve Iraq, Israel and Lebanon as well as the United States and Iran, with the possibility of western Gulf States being involved as well.
"Military deaths in (the) first wave of attacks against Iran would be expected to be in the thousands, especially with attacks on air bases and Revolutionary Guard facilities," said the report by Paul Rogers of the University of Bradford.
"Civilian deaths would be in the many hundreds at least," it said. "If the war evolved into a wider conflict, primarily to pre-empt or counter Iranian responses, the casualties would eventually be much higher."
Secret nuclear bomb
Western states suspect Iran of secretly aiming to build a nuclear bomb. Tehran, however, says its nuclear facilities are intended to produce only electricity.
"If the war evolved into a wider conflict, primarily to pre-empt or counter Iranian responses, the casualties would eventually be much higher."
The Oxford Research Group report
Washington and Jerusalem have said they would prefer to solve the dispute through diplomacy but have not ruled out military action.
The report said an attack by the United States or Israel on Iran would probably spur Tehran to work as rapidly as possible towards developing a nuclear military option.
It said US forces, already tied down in Iraq, would have a limited number of military options when dealing with Iran and would have to rely almost entirely on the air force and navy.
Any attack would almost certainly unify Iran and bolster the government in Tehran, and would mean that any future US relationship with Iran would have to be based on violence, the report said.
A military response to the crisis would be a "particularly dangerous option and should not be considered further", the report concluded.