The UN nuclear watchdog’s chief inspector will travel to Iran next week to demand co-operation from Tehran with an inquiry into uranium traces that were found at an undeclared site.
Cornel Feruta, acting chief of the International Atomic Energy Agency, said an explanation given by Iranian authorities did not seem reasonable.
Mr Feruta he told Tehran in September that “time is of the essence” in clearing up the matter.
Last year Israeli Prime Minister Benjamin Netanyahu claimed that a “secret atomic warehouse” held 15 kilograms of radioactive material, which had since been removed.
The agency investigated the site and two weeks ago confirmed samples showed traces of uranium that was processed but not enriched.
“We have continued our interactions with Iran since then but have not received any additional information and the matters remains unresolved,” Mr Feruta told an agency meeting in Vienna.
“A meeting between the agency and Iran is scheduled next week in Tehran to discuss it further. It is essential that Iran works with the agency to resolve the matter properly."
Massimo Aparo, head of the agency's protection department, will lead the delegation. Argentine Rafael Grossi is due to take charge of the agency on December 3.
In May 2018, the US withdrew from the 2015 nuclear between Tehran and world powers, which was enacted to limit Iran’s nuclear abilities, and hit the regime with sanctions.
Iran has since begun to breach sections of the treaty.
“That Iran has failed to sufficiently address this issue for close to a year is wholly unacceptable,” the US told the agency's board.
“That there are possible undeclared nuclear materials present and activities ongoing in Iran still today is profoundly concerning."
EU powers continue to voice support for the nuclear deal but have tried and failed to help Iran’s economy find a way around the sanctions.
Tehran has threatened to withdraw from the nuclear deal if a resolution is not found.
