Iran has shot down an unmanned U.S. spy plane over its Fordu nuclear site, a state-run website reported on Wednesday, a day after it confirmed it was installing a new generation of advanced uranium enrichment centrifuges.

"An unmanned U.S. spy plane flying over the holy city of Qom near the uranium enrichment Fordu site was shot down by the Revolutionary Guards' air defense units," MP Ali Aghazadeh Dafsari was quoted as saying by the Youth Journalists Club, affiliated to Iran's state TV.

"The plane ... was trying to collect information about the site's location ," he said, without giving details. He did not say when the incident happened.

The Fordu site, secretly built inside a mountain bunker near Qom, was acknowledged by Iran only after Western intelligence agencies identified it in 2009.

Iranian Foreign Ministry spokesman Ramin Mehmanparast on Tuesday appeared to confirm a Reuters story last week that Iran was installing two more advanced models of the centrifuges used to refine uranium for large-scale testing at a research site.

In January Iran announced it had shot down two unmanned western reconnaissance drone aircraft in the Gulf.

The Pentagon denied that report but acknowledged some spy planes had crashed in the past due to mechanical failure.

Iran is at odds with major powers over its nuclear work, which the United States and its allies say are intended to enable Iran to produce bombs. Iran denies the allegations and
says it wants only to generate electricity.

The United States and Israel have not ruled out military action if diplomacy fails to end the nuclear row.

Iran has dismissed reports of possible U.S. or Israeli plans to strike Iran, warning that it will respond by attacking U.S. interests in the Gulf and Israel if any such assault was made.

Analysts say Tehran could retaliate by launching hit-and-run strikes in the Gulf and by closing the Strait of Hormuz. About 40 percent of all traded oil leaves the Gulf region through the strategic waterway.

Iran often launches military drills in the country to display its military capabilities amid persistent speculation about a possible U.S. or Israeli strike on Iran's nuclear facilities.