IAEA headquarters
IAEA headquartersiStock

Inspectors from the UN’s atomic watchdog, the International Atomic Energy Agency, have confirmed Iran has started building an underground centrifuge assembly plant after its previous one exploded in what Tehran called a sabotage attack over the summer, the agency’s head told The Associated Press on Tuesday.

Iran also continues to stockpile greater amounts of low-enriched uranium, but does not appear to possess enough to produce a weapon, said IAEA Director-General Rafael Grossi.

Following the July explosion at the Natanz nuclear site, Tehran said it would build a new, more secure, structure in the mountains around the area. Satellite pictures of Natanz analyzed by experts have yet to show any obvious signs of construction at the site in Iran’s central Isfahan province.

“They have started, but it’s not completed,” Grossi told AP. “It’s a long process.”

He would not give further details, saying it’s “confidential information.”

Iran’s mission to the United Nations did not immediately respond to a request for comment.

On July 2, Iran reported an "incident" at the Natanz complex, but said it caused no casualties and failed to stop enrichment work at the facility.

An unnamed Middle Eastern intelligence official later told The New York Timesthat Israel was responsible for the attack, which he said was carried out using a powerful bomb. Israel has not commented on the report.

A member of the Iranian Parliament's National Security Committee said recently the blast at Natanz was caused by a "security breach".

Commenting on the 2015 nuclear deal between Iran and western powers, Grossi said Iran has continued to allow IAEA inspectors full access to its nuclear facilities, including Natanz, even as it has been steadily exceeding the deal’s limits in response to the US withdrawal from the agreement.

The agency said in its most recent report on Iran that the Islamic Republic’s stockpile of enriched uranium now stands at more than ten times the limit set down in the 2015 nuclear deal with world powers.

The limit was set at 300 kilograms (661 pounds) of enriched uranium in a particular compound form, which is the equivalent of 202.8 kg of uranium, while Iran's stockpile as of September stood at over 2,105 kg.

In the next report, due in coming weeks, Grossi said, “We continue to see the same trend that we have seen so far.”

The IAEA’s current assessment is, however, that Iran does not at the moment possess a “significant quantity” of uranium — defined by the agency as enough to produce a bomb — said Grossi.

“At the moment, I’m not in contact with my inspectors, but by memory, I wouldn’t say so,” he said.