Diplomats in Vienna say IAEA inspectors in Iran have found evidence of a nuclear capability that the country did not reveal in its recent disclosures, which it said included all aspects of its nuclear program.
Diplomatic sources say Iran has failed to fully inform the International Atomic Energy Agency of its nuclear activities.
Last year, Iran gave the agency what it claimed was an accurate and comprehensive report of its nuclear program.
But now, western diplomats, speaking on the condition of anonymity, say Tehran has kept secret, highly sensitive designs for uranium enrichment centrifuges that could be used to make material for nuclear weapons.
Last November, the IAEA board of governors passed a resolution saying that further serious Iranian failures to disclose any aspect of its nuclear program would lead to an immediate emergency meeting to consider all possible options.
At the time, the head of the IAEA, Mohamed ElBaradei, said that could include referring the issue to the U.N. Security Council, but that other options would also be considered.
Diplomats say much will depend on Mr. ElBaradei's advice to the board. Mr. ElBaradei has recently warned of the dangers of a global black market in nuclear components.