"Currently, the enrichment capacity of the country has reached more than twice the entire history of this industry," Mohammad Eslami, head of the Atomic Energy Organization of Iran, was quoted as saying by state news agency IRNA.

"Nuclear energy and atomic power production have great economic savings for the country and are effective in reducing fossil and non-renewable fuel consumption and environmental problems," he added, according to AFP.

The Vienna-based International Atomic Energy Agency (IAEA) said Wednesday that a technical team will visit Iran on Sunday to try to resolve a deadlock over the detection of traces of radioactive material at sites not declared as having hosted nuclear activities.

IAEA chief Rafael Grossi is not expected to be part of the delegation.

The UN nuclear watchdog has long called on Iran to explain the presence of man-made uranium found at three undeclared sites, requesting "access to locations and materials" as well as the collection of samples.

Eslami said on December 9 that the material detected at the three sites had been brought into Iran from abroad.

The issue has seriously hindered efforts to revive a 2015 nuclear deal between Iran and major powers, which has hung by a thread since the United States unilaterally withdrew in 2018 under then-president Donald Trump.

An IAEA delegation had initially planned to travel to Tehran last month, but the visit was postponed as the agency's board of governors censured Iran for failing to provide "technically credible" answers.

Under the 2015 deal, Iran agreed to restrict its enrichment of uranium to just under four percent, well below the 90 percent level considered necessary for a nuclear warhead.

In return for that and other curbs on its nuclear activities, Iran was promised relief from international sanctions.