The UN nuclear watchdog says uranium of a man-made origin has been discovered "at a location in Iran not declared to the agency," and has also confirmed that Tehran is now enriching uranium at its underground Fordo facility, a move prohibited by 2015 nuclear deal.
The revelation from International Atomic Energy Agency is the first time it has acknowledged in a report that allegations made by the U.S. and Israel against Iran are true.
The IAEA did not identify the site in the confidential quarterly report distributed to member states and seen by The Associated Press on Monday.
However, Israel and the U.S. say the site was on the outskirts of Tehran, a location previously described by Israeli Prime Minister Benjamin Netanyahu as a "secret atomic warehouse."
Israel has alleged that material at the site comes from an Iranian military program involving work on nuclear weapons. Iran denies pursuing nuclear weapons and says its program is peaceful.
The nuclear deal had called for Fordo to become a research center. It is now home to more than 1,000 centrifuges.
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In the confidential quarterly report distributed to member states, the IAEA said Iran's stockpile of low-enriched uranium still exceeds the amount allowed by the Joint Comprehensive Plan of Action, or JCPOA. The report was seen Monday by The Associated Press.
It also said Iran continues to enrich uranium up to 4.5%, above the 3.67% allowed.
The agency says 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.
A joint statement by the Foreign Ministers of France, Germany, United Kingdom and the EU High Representative on the JCPOA said the signatories are "extremely concerned" by the revelations and urged Iran to reverse all measures inconsistent with the JCPOA.
"We underline the importance of the full and effective implementation of the JCPOA by all sides and confirm our determination to continue all efforts to preserve the agreement," they said.
Since the U.S. 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.