The head of the International Atomic Energy Agency (IAEA), the UN nuclear watchdog, on Thursday chided Iran for exceeding for the second time an agreed upper limit for nuclear material set out in last year's deal with world powers, AFPreports.
A report by the IAEA last week showed that Iran's stock of so-called heavy water had inched above the 130-ton level set out in the landmark deal.
Heavy water, a modified form of normal water, is used in certain types of nuclear reactor. Plutonium for use in nuclear weapons can be extracted from fuel rods used in heavy water reactors.
"Iran has since made preparations to transfer a quantity of heavy water out of the country" which will bring it below the ceiling, IAEA chief Yukiya Amano told the agency's board on Thursday.
"It is important that such situations should be avoided in future in order to maintain international confidence in the implementation" of the deal, he added, according to AFP.
The July 2015 nuclear deal between Iran and six major powers states that Iran's "needs" are 130 metric tons of heavy water and that any excess must be "made available for export".