Iran has informed the International Atomic Energy Agency that it plans to install more than 6,000 extra uranium-enriching centrifuges at its enrichment plants and bring more of those already in place online, a confidential report by the U.N. nuclear watchdog said on Thursday.

The report seen details what Iran meant when it said it would add thousands of centrifuges in response to a resolution against it that the IAEA's 35-nation 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.