VIENNA - Building a second uranium enrichment site is a political message from Iran that neither sanctions nor possible military attack will ever halt its nuclear program, a senior Iranian official said on Tuesday.

In an interview, Ali Asghar Soltanieh, Iran's envoy to the U.N. nuclear watchdog, told Reuters the agency's concern Tehran may be hiding more nuclear work after it unveiled the enrichment site was an unfair political judgment beyond its mandate.

He said Iran's disclosure in September of the Fordow site near Qom, being built in case its main Natanz enrichment plant was bombed, showed it was heeding transparency obligations to the International Atomic Energy Agency. The IAEA feels Iran was legally bound to reveal the project at least two years ago.

In a report on Monday, the IAEA said Iran's acknowledgement of the Fordow centrifuge plant's existence was long overdue and reduced confidence that Tehran was not concealing other sites -- possibly support facilities for Fordow.

It said Iran had told the IAEA it started building the plant within a bunker beneath a mountain in the second half of 2007, but the IAEA had satellite pictures and intelligence evidence indicating construction work got under way as early as 2002.

Iran granted IAEA inspectors full access to the site on October 26-27 but not to the plant's director and original designers. The report said Iran had not yet convincingly ruled out the existence of more covert nuclear sites or plans for any.

Referring to the skepticism voiced in the IAEA report, Soltanieh said We reject this 100 percent. This kind of judgment is unfair, political and beyond the (IAEA's) mandate.

The new Fordow site is a clear political message that neither U.N. Security Council sanctions nor the threat of military attack can stop (our) enrichment under full scope safeguards of the IAEA, he said.

So the advice to those (Western powers) who have so far not coped with this reality is to cope with this reality -- that this enrichment will continue at any price under IAEA (monitoring) for peaceful purposes.

This is a contingency site, complementary to Natanz, in order that our enrichment process will never, ever be suspended. Its purpose is just to have a more protected, secure site.

Iran says the site, like the rest of its nuclear program, is meant only to yield fuel for civilian power plants.

Western nuclear analysts say the site's small size makes it unsuitable for any purpose but to enrich smaller quantities of uranium suitable for a bomb. Their suspicions rest on Iran's history of nuclear secrecy and restricting IAEA inspections.

(Reporting by Mark Heinrich; editing by Tim Pearce)