TEHRAN (Reuters) - Iran test-fired missiles on Sunday to show it was prepared to head off any military threat, four days before the Islamic Republic is due to hold rare talks with world powers worried about its nuclear ambitions.

The missile maneuvers coincide with escalating tension in Iran’s nuclear row with the West, after last week’s disclosure by Tehran that it is building a second uranium enrichment plant.

News of the nuclear facility south of Tehran added a sense of urgency to a crucial meeting in Geneva Thursday between Iranian officials and representatives of six major powers, including the United States.

Iran will be put “to the test” in Geneva and a move to sanctions would follow if the talks failed, U.S. Secretary of State Hillary Clinton told CBS.

An Iranian official warned “fabricated Western clamor” over the new plant would negatively affect the talks at which the six powers want Iran to agree to open its facilities to inspection to prove its program is for power and not nuclear weapons.

Ali Asghar Soltanieh, Iran’s envoy to the U.N.’s nuclear watchdog, said, referring to Western condemnation of the plant: “This ... approach will have a negative impact on Iran’s negotiations with the 5+1 countries.”

He has said Iran is arranging International Atomic Energy Agency inspections of the plant “in the very near future.”

U.S. President Barack Obama said Saturday the discovery of the secret nuclear plant in Iran showed a “disturbing pattern” of evasion by Tehran. He warned Iran Friday it would face “sanctions that bite” if it did not come clean.

Earlier this month, Obama dropped a Bush-era plan to deploy missiles in Poland that had been proposed as a shield amid concerns Iran was trying to develop nuclear warheads it could mount on long-range missiles.

Iranian media said Revolutionary Guards launched at least two types of short-range missiles on the exercise’s first day on Sunday in central Iran and tested a multiple missile launcher.

“For all those who ... might harbor dreams about undertaking military invasion against our nation and country, a message of this maneuver is firmness, destructiveness, real and endless resistance,” Iranian General Hossein Salami, head of the Guards’ air force, told state television.

Iranian media said medium-range Shahab 1 and 2 missiles, which officials say have a range of 300 and 500 km respectively, would be test-fired Sunday evening.

State radio said the Guards Monday would test-fire the Shahab 3 missile, which Iranian officials say has a range of around 2,000 km, potentially putting Israel and U.S. bases in the Gulf within reach. It was last tested in mid-2008.

Slideshow ( 8 images )

Iran conducts war games or tests weapons to show its resolve to counter any attack by foes like Israel or the United States.

U.S. Defense Secretary Robert Gates, who says any military action against Iran would only “buy time” and stresses the need for diplomacy, told CNN he hoped the disclosure of the second facility would force Tehran to make concessions.

“The Iranians are in a very bad spot now because of this deception,” he said.

Slideshow ( 8 images )

VAPOR TRAILS

State television showed footage of missiles soaring into the sky in desert-like terrain, leaving vapor trails, in the drills held during Iran’s Holy Defense Week marking the start of the 1980-88 Iran-Iraq war.

Andrew Brookes, of the International Institute for Strategic Studies think-tank in London, told Reuters by phone he believed the missile tests had long been planned and were not a response to Western condemnation of the second enrichment plant.

But he noted the firing of the missiles came before the Geneva talks, adding Tehran was showing “we are a powerful nation, we need respect ... we are coming as equals.”

English-language Press TV said the weapons tested Sunday included a ground-to-ground missile and a naval missile, naming them as Fateh (Victorious) and Tondar (Thunder).

The United States, which suspects Iran is seeking to build nuclear bombs, has previously expressed concern about Tehran’s missile program. Iran says its nuclear work is solely for peaceful power generation purposes.

Neither the United States nor its ally Israel have ruled out military action if diplomacy fails to resolve the nuclear row.

Iran has said it would respond to any attack by targeting U.S. interests in the region and Israel, as well as closing the Strait of Hormuz, a vital route for world oil supplies.

Iran acknowledged the existence of the enrichment plant near the holy city of Qom for the first time Monday to the International Atomic Energy Agency, the U.N. nuclear watchdog.

U.S. officials said the disclosure was designed to pre-empt an announcement by Western governments, which were aware of the site, but Iranian President Mahmoud Ahmadinejad said the plant was legal and open for inspection by the IAEA.

A senior U.S. administration official said the six powers -- the United States, Russia, Britain, France, China and Germany -- were preparing “a set of transparency demands” focused on the uranium enrichment plant near Qom.

“Those demands include unfettered access for the IAEA to the Qom facility, the people working there, and timelines related to its development,” the official said.