The International Atomic Energy Agency says Iran has failed to provide details of its plans to resume nuclear fuel research next week.
Spokeswoman Melissa Fleming says a meeting was scheduled in Vienna Thursday to discuss the issue, but that the Iranian delegation did not show up for it.
She added that IAEA chief Mohamed ElBaradei is still seeking clarification from Iran about its plan to resume nuclear fuel research on Monday.
In Washington, U.S. Secretary of State Condoleezza Rice expressed hope that talks between Iran and European negotiators can resolve the nuclear dispute. But she warned that if talks fail, there is strong international support to refer Iran to the U.N. Security Council for possible sanctions.
Washington accuses Tehran of secretly pursuing nuclear weapons, a charge Tehran denies.
Some information for this report was provided by AP, and Reuters.