Iran had stated that it had suspended production of centrifuge components as of April 9.
The International Atomic Energy Agency "has been able to confirm this at three workshops but three workshops belonging to private companies have continued production," the IAEA said in a report, which diplomats read to AFP.
The IAEA said the workshops claimed they had not been given compensation for stopping production.
It also said Iran has now admitted to importing "some" magnets for sophisticated P-2 centrifuges, which can be used to make bomb-grade highly enriched uranium, despite having previously said it had not obtained any P-2 centrifuges or parts from abroad, having made these domestically.
The IAEA said Iran has admitted to having inquired to buy 4,000 magnets for P-2 centrifuges, enough for 2,000 centrifuges, although it had not bought any.