Diplomats say Iran is readying a new phase of uranium processing, despite a call by the U.N. atomic agency to suspend all sensitive nuclear work.
Officials at the International Atomic Energy Agency said Iran will begin feeding a new batch of uranium into its plant at Isfahan next week.
Earlier this year, the 35-nation IAEA board warned it would refer Iran to the U.N. Security Council if the country failed to suspend uranium enrichment and allow nuclear inspections.
This week, Iran allowed U.N. inspectors access to its Parchin military complex to collect environmental samples, in an apparent effort to avoid possible sanctions.
The United States says the Parchin site has been used for nuclear weapons testing. But Tehran insists its nuclear program is peaceful.
Meanwhile, Iran's state media quoted the country's foreign minister saying more than 40 of the country's ambassadors were being replaced. He said some envoys had reached retirement age, adding their terms will expire by the end of the year.