The Director General of the International Atomic Energy Agency (IAEA), Rafael Grossi, arrived in Tehran on Saturday to discuss Iran’s nuclear program after discovering particles of uranium enriched to a level close to making an atomic bomb.

Grossi was received at the airport by the Atomic Energy Organization of Iran spokesman Behrouz Kamalvandi.

During his two-day visit, Grossi is scheduled to meet President Ebrahim Raisi, the head of the Atomic Energy Organization, Mohammed Eslami, and other officials.

According to a confidential IAEA report seen by AFP this week, uranium particles enriched up to 83.7 percent, just under the 90 percent needed to produce an atomic bomb, had been detected at Iran’s underground Fordow plant, south of Tehran.

Iran denies its desire to acquire nuclear weapons. It justified the matter by referring to “unintended fluctuations” during the enrichment process, stressing that it had not attempted to enrich uranium beyond 60 percent purity.

France, a signatory to a 2015 deal, described the new enrichment development on Thursday as “unprecedented and extremely serious.”

According to a diplomatic source in Vienna, Grossi will seek to secure more substantial access to the site during his visit and increase the number of inspections.

The Agency said Grossi would speak to the press upon returning to Vienna Saturday.

Grossi last visited Iran in early March 2022, in a trip focused on the sites, when it seemed likely that an agreement would be reached to resume negotiations between the major powers and Tehran on the nuclear file.

But in a volatile geopolitical context caused by the war in Ukraine, this opportunity was lost. The US, Europe, and other countries, such as Israel, expressed growing concerns over Iran’s progress toward producing a nuclear bomb.

The Head of IAEA aimed to “relaunch the dialogue” as Iran gradually backed down from the obligations of the agreement concluded in 2015 to limit its nuclear activities in exchange for lifting international sanctions.

Tehran is doubling the number of centrifuges at its sites and continues to enrich uranium at high levels.

The IAEA Board of Governors denounced Iran’s lack of cooperation regarding discovering traces of enriched uranium found in three undeclared sites.

For his part, CIA Director William Burns expressed his concern about the sudden progress of the Iranian nuclear program, saying it is growing at a worrisome pace.

“They’ve advanced very far to the point where it would only be a matter of weeks before they can enrich to 90% if they chose to cross that line.”

However, he added that the US does not believe that Iranian Supreme Leader Ali Khamenei has decided to resume the weaponization program that “we judge that they suspended or stopped at the end of 2003.”

Burns also expressed concern about the growing partnership between Russia and Iran, noting that aid shared between Russia and Iran may go beyond the supply of drones and ammunition.