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 drive 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 site during talks with a senior IAEA team earlier this year. Western diplomats suspect the Islamic state may now be trying to clean up the facility.
The six powers are the United States, China, Russia, France, Germany and Britain.