"You, who have used nuclear weapons against innocent people, who have used uranium ordnance in Iraq, should be tried as war criminals in courts," Mahmoud Ahmadinejad said in an apparent reference to the United States.

Ahmadinejad did not elaborate, but he apparently was referring to the U.S. military's reported use of artillery shells packed with depleted uranium, which is far less radioactive than natural uranium and is left over from the process of enriching uranium for use as nuclear fuel.

Since the Iraq war started in 2003, American forces have fired at least 120 tons of shells packed with depleted uranium, an extremely dense material used by the U.S. and British militaries to penetrate tank armor. Once fired, the shells melt, vaporize and turn to dust.

"Who in the world are you to accuse Iran of suspicious nuclear armed activity?" Ahmadinejad said during a nationally televised ceremony marking the 36th anniversary of the establishment of Iran's volunteer Basij paramilitary force.

Iran has been under intense international pressure to curb its nuclear program, which the United States claims is part of an effort to produce nuclear weapons. Iran denies such claims and says its program is aimed at generating electricity.

Iran insists that it has the right to fully develop the program, including enrichment of nuclear fuel — a process that can produce fuel for nuclear reactors or atomic bombs.

On Thursday, the European Union accused Iran of having documents that show how to make nuclear warheads and joined the United States in warning Tehran it could be referred to the U.N. Security Council for possible sanctions.

Iran has temporarily stopped its enrichment program, but negotiations with Britain, France and Germany broke off in August after Tehran restarted another part of its program: the conversion of raw uranium into the gas that is used as the feeder stock in enrichment.

Iran also has rejected European calls to halt work at its uranium conversion facility near the central city of Isfahan.

Ahmadinejad dismissed Western concerns over his country's nuclear program.

"They say Iran has to stop its peaceful nuclear activity since there is a probability of diversion while we are sure that they are developing and testing (nuclear weapons) every day," Ahmadinejad said. "They speak as if they are the lords of the world."

State-run TV said more than 9 million Basij members formed human chains in different parts of the country to mark their militia's anniversary. Thousands linked hands to make a 12-mile chain along an expressway in northern Tehran.

Some Basij members also formed chains around an enrichment plant in the central city of Natanz and a nuclear plant under construction in the southern city of Bushehr, symbolizing their readiness to defend the country's nuclear program, Iranian TV reported.

It is estimated that the Basij comprise 15 percent of Iran's population, or about 10 million people.