Last month a senior U.S. official said the United States and its allies would demand that Iran halt higher-grade enrichment and immediately close the Fordow facility at talks over Tehran's nuclear standoff with the West.
The New York Times reported that negotiators for Western countries would press Iran to ultimately dismantle the site near the city of Qom, which has been used to expand the higher-grade enrichment the Islamic Republic began just over two years ago.
But Iran's ambassador to the International Atomic Energy Agency, Ali Asghar Soltanieh, told Reuters he saw "no justification" for closing Fordow, which he said was under IAEA surveillance.
"When you have a safe place, secure place under IAEA control, then why do you tell me that I should close it?" he said, making clear Iran built the site to better protect its nuclear program against any Israeli or U.S. attacks.
"Fordow is a safe place. We have spent a lot of money and time to have a safe place," Soltanieh added.
Iran and major powers resumed talks in mid-April in Istanbul after a gap of more than a year - a chance to ease escalating tension and help to avert the threat of a new Middle East war. They are to meet again on May 23 in Baghdad.
The West says Iran's nuclear work is a cover for developing atomic bombs and wants verifiable assurances to the contrary from Tehran - for example, by accepting much more intrusive U.N. nuclear inspections and limiting its enrichment capacity.
IRAN "OPTIMISTIC" ABOUT TALKS
Iran denies having a weapons agenda, saying it is enriching uranium solely for peaceful energy purposes. Refined uranium can be used to fuel nuclear power plants, which is Iran's stated aim, or provide the core for a bomb if processed more.
"One thing is clear: the enrichment in Iran will never be suspended," Soltanieh said.
He declined to comment however on Western demands that Iran halt the higher-grade enrichment, to a fissile concentration of 20 percent, it started in 2010 and has since sharply increased, shortening the time needed for any nuclear weapons breakout.
The U.N. Security Council has demanded in a series of resolutions since 2006 that Iran suspend all enrichment but Western diplomats have indicated the immediate priority is to get it to cease the more sensitive higher-grade work.
Many analysts say it will be possible to find a negotiated solution to the long-running row only if both sides compromise: Iran would be allowed to continue some lower-level enrichment if it accepts more far-ranging U.N. inspections.
Iranian officials say they are optimistic that the talks with United States, Russia, China, Germany, France and Britain will make progress and they underline their expectations that the negotiations will lead to an end of sanctions.
However, the United States and its allies have made clear Tehran must take action to allay their concerns about its nuclear ambitions before they can consider relaxing sanctions.
Western states have imposed expanded, more biting sanctions against Iran's energy and banking sectors since the beginning of this year. The European Union is preparing to slap a total embargo on the purchase of Iranian crude oil in July.
Soltanieh said the sanctions could not stop Iran's nuclear program: "Neither sanctions, nor military actions, nor terror against our scientists will stop the enrichment."
