The International Atomic Energy Agency says Iran has obtained instructions from international smugglers for making nuclear weapons components.
The IAEA accusation is included in a report for presentation to the 35-nation IAEA board Thursday in Vienna.
The report, obtained by Western journalists, also confirms that Tehran has begun renovation work at a key nuclear plant, but has not yet begun actual uranium enrichment work.
European and U.S. officials accuse Iran of seeking high-grade enriched uranium to make an atomic bomb, but Tehran insists it is seeking a lower grade to make electricity.
Tuesday, Britain, the United States, China, Russia and France said the IAEA should refer Iran to the United Nations Security Council for allegedly violating a key nuclear treaty with its atomic program.
However, Iran's Foreign Minister said U.N. inspectors will be barred from its nuclear facilities starting Saturday if a referral is made.
Some information for this report was provided by AFP, AP and Reuters.