Updated

TEHRAN, Iran -- Iran has dug mass graves in which to bury U.S. troops in case of any American attack on the country, a commander of the elite Revolutionary Guard said Tuesday, warning that a military strike would spark an "extensive war" in the region.

The announcement appears to be a show of bravado after the chairman of the U.S. Joint Chiefs of Staff, Adm. Mike Mullen, said last week that the U.S. military has a contingency plan to attack Iran, although he thinks a military strike is probably a bad idea.

The U.S. and some of its allies accuse Iran of using its civilian nuclear program as a cover to build nuclear weapons. Iran has denied the charges, saying its nuclear program is geared merely toward generating electricity, not bomb.

The deputy commander of the Revolutionary Guard, Gen. Hossein Kan'ani Moghadam, said graves for any attacking U.S. troops have been dug in Iran's southwestern Khuzestan province, where Iran buried Iraqi soldiers killed during the ruinous 1980-88 war between the Islamic republic and Iraqi leader Saddam Hussein's regime.

"The mass graves that used to be for burying Saddam's soldiers have now been prepared again for U.S. soldiers, and this is the reason for digging this big number of graves," Moghadam said, according to the semiofficial Fars news agency.

Moghadam, however, said American troops would likely not be able to set foot on Iranian soil, repeating warnings that Iran will retaliate against U.S. bases in the Gulf if there is an attack on Iran. The U.S. Navy's 5th Fleet headquarters is based just across the Gulf from Iran in Bahrain.

"I assume that the enemy will be hit in its own military bases out of our borders and will not have any chance to have its forces land in Iran," he said.

"If the U.S. decides to take a pre-emptive action and attack Iran, Iran will have no choice but to strike the American bases in the region," he said. "The heavy costs of such a war will not be just on the Islamic Republic of Iran. America and other countries should accept that this would be the start of an extensive war in the region."

The war of words has intensified between Iran and the United States after the U.N. Security Council imposed a fourth round of tougher sanctions in June in response to Iran's refusal to halt uranium enrichment, a technology that can be used to produce nuclear fuel or material for an atomic bomb.

The U.S. and Israel have said military force could be used if diplomacy fails to stop what they suspect is an Iranian nuclear weapons program.

Iran put the Guard -- its most powerful force -- in charge of defending the country's territorial waters in the Persian Gulf in 2008. Iran has sought to upgrade its air defense systems and naval power, saying any possible future attacks against Iran will be air and sea-based.