VIENNA, June 5 (Reuters) – The U.N. nuclear watchdog expressed serious concern on Tuesday that Iran has continued for months to deny it access to sites of interest to it, describing previous suspected activities there that could have been part of a nuclear weapons programme.

The IAEA issued a report in March admonishing Iran for failing to answer its questions about past nuclear activities at three sites and for denying it access to two of them. Diplomats have since said that the agency is looking into activities at the sites that predate its 2015 deal with major powers.

A report to IAEA member states issued on Tuesday detailed suspected activities and materials including “the possible presence…of natural uranium in the form of a metal disc” at a site that “underwent extensive sanitization and levelling in 2003 and 2004”, the report said, describing the third site.

U.S. intelligence agencies and the IAEA believe Iran had a secret, coordinated nuclear weapons programme that it halted in 2003.

“The (IAEA) director general calls on Iran immediately to cooperate fully with the agency, including by providing prompt access to the locations specified,” the IAEA report said.

That report was in addition to a regular quarterly report that showed the Islamic Republic remains in breach of many of the restrictions imposed by its nuclear deal with major powers, and that its stockpile of low-enriched uranium has increased by roughly half to 1,571.6 kg, well above a 202.8 kg limit.

Iran began breaching the accord after President Donald Trump withdrew the United States from the deal – reached before he took office – in 2018 and reimposed heavy economic sanctions on Tehran.

(Reporting by Francois Murphy Editing by Mark Heinrich)