The UN nuclear watchdog is to discuss with Iran the discovery of uranium traces at an undeclared site in Tehran next week, the agency’s acting chief said on Thursday. Iran had not provided any more information about the origin of the particles, according to the International Atomic Energy Agency.

The IAEA found the traces of uranium at the site that Israeli PM Benjamin Netanyahu drew attention to in a speech last year, calling it a “secret atomic warehouse,” Reuters reported in September.

Tehran has said the site is a carpet-cleaning facility. Two weeks ago the IAEA confirmed to member states that environmental samples taken at the site had shown traces of natural uranium that was processed by human activity but had not been enriched.

“We have continued our interactions with Iran since then, but have not received any additional information and the matter remains unresolved,” IAEA acting chief Cornel Feruta told a quarterly meeting of his agency’s 35-nation Board of Governors.