Iran unveiled a redevelopment of part of its Arak heavy water reactor on Monday - a move that did not breach international restrictions on its nuclear work but showed it is developing the sector in the face of U.S. pressure.
Iranian state media said technicians switched on a secondary circuit at Arak, a plant built to produce the heavy water used as a moderator to slow down reactions in the core of nuclear reactors.
"Today we are ... starting a noteworthy section of the reactor," the head of Iran's atomic agency, Ali Akbar Salehi, said in remarks broadcast live on state TV.