The December 18 visit by Yukiya Amano, the head of the International Atomic Energy Agency (IAEA), came just days after the U.S. Congress voted to extend some sanctions against Iran.
Tehran believes that constitutes a breach of the deal that was negotiated by the United States, Russia, China, and other world powers.
Iran's President Hassan Rohani said Tehran would abide by the deal if other countries did as well, and said the watchdog agency reports should be "technical and impartial."
The IAEA said last month that Iran exceeded production limits on heavy water by 100 kilograms over the 130 metric tons allowed under the agreement.
Heavy water is used to cool reactors that produce plutonium, one component of nuclear bombs.