The diplomat said a European Union-sponsored resolution aimed at increasing pressure on Iran to improve its cooperation with an International Atomic Energy Agency probe of its nuclear programme was passed by the 35-nation IAEA board.
Twenty-seven members voted in favour of the motion, five abstained and three voted against, a diplomat said.
The resolution also says Iran must reinstate a freeze of activities related to small-scale enrichment of uranium. Iran has so far disregarded calls for it to do so, pressing ahead with uranium-processing and preparing for enrichment.
That process can make fuel for power plants or atomic bombs.
Iran has threatened to respond to the move — initiated by the United States, EU powers, Russia and China — by curbing U.N. inspections of its nuclear facilities and scrapping talks on a Russian compromise proposal.