The International Atomic Energy Agency report seen by Reuters details what Iran meant when it said it would add thousands of centrifuges in response to a resolution against it that the IAEA's Board of Governors passed last week at the request of Britain, France, Germany and the United States.

More enrichment capacity means Iran can enrich uranium more quickly, potentially increasing the nuclear proliferation risk. Iran denies seeking nuclear weapons but Western powers say there is no civil explanation for enriching uranium to up to 60% purity, close to the roughly 90% that is weapons grade, which no other country has done without producing a nuclear bomb.

The only enrichment level specified for new centrifuges is 5% purity, far from the 60% Iran is already producing. The lower purity, particularly at its Fordow site, could be seen as a conciliatory move by Iran as it seeks common ground with European powers before the return of US President-elect Donald Trump, though enrichment levels can be changed easily later, Reuters said.