The United Nations’ nuclear watchdog said it has detected uranium particles at an undeclared site in Iran in its latest report on the country’s nuclear program issued on Monday.

The report from the International Atomic Energy Agency (IAEA), seen by AFP, says: “The agency detected natural uranium particles of anthropogenic origin at a location in Iran not declared to the agency.”

The particles are understood to be the product of uranium which has been mined and undergone initial processing, but not enriched.

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The IAEA added that it was “essential for Iran to continue interactions with the agency to resolve the matter as soon as possible.”

While the IAEA itself has not named the site in question, diplomatic sources have previously said the agency has been posing questions to Iran relating to a site where Prime Minister Benjamin Netanyahu has alleged secret atomic activity.

Sources said the IAEA took samples from the site in the Turquzabad district of Tehran in the spring.

The revelation from International Atomic Energy Agency is the first time it has acknowledged in a report that allegations made by the US and Israel against Iran are true.

Bloomberg reported Thursday that a senior IAEA official had told diplomats in a closed-door meeting in Vienna that the Islamic Republic was “evading attempts to discover the source of man-made and natural uranium particles detected at a warehouse in Tehran.”

In September, the Reuters news agency reported that traces of uranium had been found at the facility on the outskirts of Tehran that was alleged by Netanyahu to be a “secret atomic warehouse.” The IAEA reportedly confirmed that detail last week to member states.

The IAEA report also confirmed that Iran has ramped up uranium enrichment, with AFP reporting that it stated that the stockpile of enriched uranium now reaching the equivalent of 551 kilograms, as opposed to the 300-kilogram limit laid down in Iran’s 2015 deal with world powers.

According to the Associated Press, the IAEA reported that as of November 3, Iran’s stockpile of low-enriched uranium was 372.3 kilograms (820.78 pounds) compared to 241.6 kilograms reported on August 19, and past the 202.8 kilogram limit.

The report also confirmed that Iran is now enriching uranium at its underground Fordo facility, a move prohibited by 2015 nuclear deal.

Iran invited inspectors from the International Atomic Energy Agency to Fordo to see its work.

The nuclear deal had called for Fordo to become a research center. It is now home to more than 1,000 centrifuges.

Since the US pulled out of the Iran nuclear pact last year and imposed sanctions, Iran has been slowly violating its provisions to pressure other nations to provide more incentives.