The International Atomic Energy Agency and Iran failed in two days of discussions last week to agree a framework deal to resume a long-stalled IAEA investigation into suspected nuclear bomb research in the Islamic state.
The IAEA said after the January 16-17 negotiations that the two sides would meet again on February 12 in Tehran. An IAEA spokeswoman said the date had now been changed, giving no further details.
The U.N. agency has been trying for a year to negotiate an agreement that would give its inspectors access to sites, officials and documents in Iran.
Western diplomats accuse Iran of stonewalling the IAEA investigation. Iran denies Western accusations that it is seeking to develop the capability to make nuclear weapons, saying its atomic activities are aimed at generating electricity.
(Reporting by Fredrik Dahl; Editing by Janet Lawrence)