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International nuclear monitors have started conducting unannounced inspections at a uranium enrichment site in Iran after it hiked levels closer to weapons-grade last year.

The International Atomic Energy Agency reported late Wednesday its staff had been granted the authority to conduct the snap inspections at Iran’s mountainside enrichment facility in Fordow.

Iran says its nuclear work is for peaceful purposes but Western and regional countries say it’s aiming to build an atomic weapon. They also cite concerns over its conventional military advances. On Thursday Iran blamed Israel for attacking a munitions depot last weekend with drones, in an attack that has escalated tensions in the Middle East.

Iran Blames Israel for Drone Attack and Hints At Response

Inspectors discovered modifications that should have been reported during a surprise visit to the plant last month, the IAEA said.

Despite stonewalling an IAEA investigation into past nuclear activities and removing some monitoring equipment, Iran continues sites allowing expansive inspections, it said.

“The Agency has had regular access to Fordow Fuel Enrichment Plant and continued to monitor and verify Iran’s enrichment-related activities at the facility,” IAEA Director General wrote in the 2-page restricted report.

Iran’s November decision to produce highly-enriched uranium at Fordow triggered a stricter set of monitoring measures to be put in place, including the possibility of snap inspections. That allowed the IAEA on Jan. 16 to detect modifications to the centrifuges at Fordow that should have been reported before the work was done. Iran amended its report on the new mode of operation on Jan. 25.

Despite ceasing to implement stricter monitoring measures imposed by its defunct nuclear deal with world powers over its program, Iran has still been subject to record IAEA inspections, according to the most recent data. The IAEA’s board of governors meets next month in Vienna to consider Iran’s program.

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