Inspectors from the United Nations nuclear watchdog found uranium particles enriched up to 83.7% in Iran’s underground Fordo nuclear site, a report seen Tuesday by The Associated Press said.

The confidential quarterly report by the Vienna-based International Atomic Energy Agency distributed to member states likely will raise tensions further between Iran and the West over its program. That’s even as Tehran already faces internal unrest after months of protests and Western anger over sending bomb-carrying drones to Russia for its war on Ukraine.

The IAEA report only speaks about “particles,” suggesting that Iran isn’t building a stockpile of uranium enriched above 60% — the level it has been enriching at for some time.

The IAEA report described inspectors discovering on Jan. 21 that two cascades of IR-6 centrifuges at Iran’s Fordo facility had been configured in a way “substantially different” to what had been previously declared. The IAEA took samples the following day, which showed particles up to 83.7% purity, the report said.

“Iran informed the agency that ‘unintended fluctuations’ in enrichment levels may have occurred during the transition period,” the IAEA report said. “Discussions between the agency and Iran to clarify the matter are ongoing.”