Six world powers called on Iran on Thursday, March 8, to let international inspectors visit a military site where the UN nuclear watchdog says development work relevant to nuclear weapons may have taken place.

According Reuters, in a joint statement at a board meeting of the International Atomic Energy Agency (IAEA), the powers also voiced "regret" about Iran's stepped-up campaign to enrich uranium - activity which can have both civilian and military purposes.

"We urge Iran to fulfill its undertaking to grant access to Parchin," the statement said, referring to the military facility southeast of Tehran. Iran refused access to the complex during two rounds of talks with a senior IAEA team earlier this year.

Western diplomats suspect the Islamic state may now be trying to clean up the site to remove evidence of research with nuclear applications before possibly allowing inspectors in.

The six powers handling the Iran nuclear issue are the United States, China, Russia, France, Germany and Britain.