VIENNA, Austria – Iranian engineers have built a secret underground storage area for use as a uranium-enrichment facility in a restricted military area of interest to the U.N. nuclear watchdog agency, an Iranian exile said yesterday.

The exile, Alireza Jafarzadeh, said the “camouflaged tunnel-like facility” was completed recently at Parchin, a sprawling Iranian military complex about 20 miles southeast of Tehran.

An Iranian official who normally speaks freely to the press refused to comment on the record about the report, saying the allegation was not worth responding to.

A senior diplomat familiar with International Atomic Energy Agency, speaking anonymously because of the sensitivity of the investigation, said the agency was unaware of such developments.

But the diplomat said if such construction did occur without notification, it would constitute a violation of an agreement by the Iranians to suspend all uranium-enrichment activity.

The freeze is in effect while Iran and European negotiators discuss ways of banishing international suspicions that Iran wants to use the technology to make nuclear weapons.

France, Germany, and Britain, the main European negotiators, insist that Iran pledge to scrap or permanently suspend its plans to enrich uranium. Tehran, which says it needs the technology to generate electricity, refuses to go beyond a suspension during the talks.

The third round of talks wound up in Paris on Wednesday with Iran refusing to mothball the program but apparently willing to maintain the temporary freeze. Mr. Jafarzadeh, asked specifically if enrichment activities were going on at the underground storage area, said his contacts, whom he described as “having access to information inside the Iranian regime,” did not know whether the equipment was just being stored or was active. Mr. Jafarzadeh is the former spokesman of National Coalition of Resistance of Iran, banned in America by Washington, which considers it a terrorist organization.

IAEA inspectors visited Parchin early this year and were allowed to take environmental samples from some of its buildings to test American allegations that Iran may be testing high-explosive components for nuclear weapons by using an inert core of depleted uranium as a dry run for a bomb that would use fissile material.

But Tehran turned down a renewed agency request to visit other parts of the site last month, arguing it was not bound under agreements with the agency to open Parchin or other facilities not clearly linked to Iran’s nuclear program to outside survey.

Mr. Jafarzadeh, who now runs the Washington-based Strategic Policy Consulting think tank, revealed key information about two hidden nuclear sites in Iran in 2002 that helped uncover nearly two decades of covert Iranian atomic activity – and sparked present fears that Tehran wants to build the bomb.