Iran re-opened part of the plant already on 8 August, after rejecting the European Union's offer of a package of economic and technology incentives if it abandons attempts to enrich uranium.
Many in the West fears Iran is using its nuclear program to secretly develop weapons.
In Vienna, the IAEA governing board was due to meet again to consider what action to take against Iran. Reports say EU diplomats are trying to persuade board members that Iran should be taken before the UN Security Council.
Amid Tough Words, Iranian And U.S. Presidents Back More Nuclear Talks