A senior U.N. official says his team made headway during talks in Tehran meant to restart an investigation of suspicions the Islamic Republic may have secretly worked on a nuclear arms program.

Herman Nackaerts says that means the U.N. nuclear agency expects to resume its probe early next year.

Nackaerts is in charge of the Iran investigation with the International Atomic Energy Agency. He spoke Friday at Vienna's airport on return from Tehran.

Iran denies any interest in nuclear weapons.

Nackaerts says "we were able to make progress" on resuming the investigation. He adds the IAEA expects to "start implementing" an agreement on the probe short after new talks in Tehran Jan. 16.