VIENNA, Sept 7, 2026 (BSS/AFP) - An undeclared Syrian nuclear reactor being constructed during the era of former leader Bashar al-Assad was "almost complete", representing an "important step" in any nuclear weapons programme, the UN nuclear watchdog said on Monday.

Inspectors from the International Atomic Energy Agency (IAEA) last month visited two sites, one in Deir Ezzor and a second undisclosed location identified to them by Syrian authorities.

In a report seen by AFP last week, the IAEA said it found that Syria's previous government was building a nuclear reactor.

Longtime ruler Assad was toppled in December 2024, bringing to power the current Islamist government.

IAEA head Rafael Grossi said it was "obvious that the previous government was pursuing a number of clandestine" activities.

"I cannot judge intentions, but it is very clear that these activities were not declared, they didn't want the world to know what they were doing," he told reporters after opening the Vienna-based agency's quarterly Board of Governors meeting.

"Given the configuration, the technical features of that type of reactor, this is a reactor that is very efficient in the production of fissile material that could be used directly for the fabrication of nuclear weapons," he said, adding that building the reactor was a "very important step".

He added that the reactor -- which is currently being excavated -- "was almost completed".

"It was in a very advanced stage of construction," he said, adding that it was "very possible and cannot be excluded that the then Syrian authorities also performed some explosions in order to... hinder any possibility of an investigation".

Besides the nuclear reactor under construction at the Deir Ezzor site, the IAEA found a fuel fabrication plant, where the nuclear fuel for the reactor was manufactured, and a location where nuclear fuel as well as uranium scrap and waste were stored.

In its report, the IAEA said it found around 73 tonnes of natural uranium metal.

Grossi has praised Damascus's "courageous decision" to report the undisclosed site.

The UN atomic watchdog had declared in 2011 that the location was "very likely" to host a nuclear reactor, adding that its information suggested it was being built with North Korean assistance.

On Monday, Grossi said it was up to the IAEA board to decide on the Syria file and that he currently had not been tasked to further investigate alleged connections to North Korea.

A draft resolution seen by AFP, expected to be submitted to the board this week for a vote, proposes closing the Syria nuclear file.

The IAEA will continue to work with Syria to keep the material safe and report its findings, Grossi said.