In a confidential report leaked to reporters on Wednesday, the International Atomic Energy Agency (IAEA) said Iran's stock of near-weapons grade uranium increased slightly before Israel attacked its nuclear facilities on June 13.
"During this reporting period, the Agency lost continuity of knowledge in relation to the current inventories of nuclear material in Iran ...which urgently needs to be addressed," the report said.
It also confirmed for the first time that two of its inspectors took documents from the Fordow site back to Vienna, calling it an "error" that led to Iran withdrawing their designation.
"The incident did not involve any breach of confidentiality," IAEA asserted, lamenting Tehran's decision to bar the inspectors involved from returning to the country.
"While these pages contained some description of the interior of the facility, they did not include content that compromised the security of the facility," the report added.
'Can't wait for months'
IAEA chief Rafael Grossi told Reuters on Wednesday that another round of talks with Iran is due in Vienna this week and emphasized the need to investigate and verify Iran’s highly enriched uranium stockpile.
"It’s not something that can drag on for months,” Grossi told Reuters. “It would be ideal to reach an agreement before next week."
Since US military strikes on three major Iranian nuclear sites on June 22, IAEA inspectors have only accessed another site that was left unscathed - the Bushehr nuclear power plant.
Following Israeli and other military strikes on Iran, the Iranian parliament passed a bill imposing restrictions on inspection and access cooperation with the IAEA.
Any new cooperation mechanism must now be approved by Iran’s Supreme National Security Council, and no agreement for inspections or resumption of IAEA work has been reached.
"We have reminded our Iranian counterparts that domestic laws create obligations for Iran, not the IAEA," Grossi said.
Grossi stressed the need to investigate Iran’s highly enriched uranium stockpile, saying no evidence suggests significant movement of the material.
“I believe there is a general understanding that the material is likely still there, but it must be verified. Some could have been lost,” he said. “We have no indications of major material movement.”
Following the activation of the UN sanctions snapback mechanism by France, Germany and the United Kingdom last week, Tehran warned of an unspecified response.