A facility in Tehran which Israel claimed was used by the Islamic republic as a “secret atomic warehouse” has been found to contain traces of uranium, Reuters reported Sunday.

The International Atomic Energy Agency (IAEA) discovered the uranium traces while investigating a facility which Israeli Prime Minister Binyamin Netanyahu cited during an address to the United Nations General Assembly last year as proof that Iran had been storing radioactive material in violation of the 2015 Iran nuclear deal.

Two diplomats with knowledge of the IAEA’s inspection work told Reuters Sunday that uranium traces had been found at the Iranian warehouse – strengthening Netanyahu’s claims Iran had secretly stored atomic material at the site.

While the IAEA had asked Iran to explain the findings, Tehran has thus far refused to respond, the two diplomats claimed.

During his address last fall, Netanyahu claimed Iran was storing 15 kilograms (33 pounds) of uranium at the storage facility, pointing to a satellite photo of the warehouse in question.

“Just last month, they removed 15 kilograms of radioactive material. You know what they did with it? They had 15 kilograms of radioactive material, they had to get it out of the site, so they took it out and they spread it around Tehran in an effort to hide the evidence.”

“Now, the Iranian officials cleaning out that site still have a lot of work to do because they’ve had at least, at least 15 ship containers, they’re gigantic, 15 ship containers full of nuclear related equipment and material stored there. Now, since each of those containers can hold 20 tons of material, this means that this site contains as much as 300 tons, 300 tons of nuclear related equipment and material.”

In April, it was reported that the IAEA was inspecting the warehouse in question, following Netanyahu’s UN address.

While previous reports have confirmed that radioactive material was found at the Tehran warehouse, the new Reuters report claims that uranium, the key element needed for producing atomic weaponry, was the radioactive material discovered.

“There are lots of possible explanations,” one of the two diplomats told Reuters, though Iran’s refusal to comment on the discovery makes it difficult for the IAEA to determine whether the traces were left from uranium stockpiles stored at the facility before or after the 2015 nuclear deal.