VIENNA, Nov 28 (Reuters) - Iran has informed the U.N. nuclear watchdog 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 watchdog said on Thursday.

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 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.

The only enrichment level specified for new centrifuges was 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 U.S. President-elect Donald Trump, though enrichment levels can be changed easily later.

Iran already has well over 10,000 centrifuges operating at two underground plants at Natanz and Fordow and an above-ground pilot plant at Natanz. The report outlined plans to install 32 more cascades, or clusters, of more than 160 machines each and a massive cascade of up to 1,152 advanced IR-6 machines.

At the same time, the number of cascades Iran plans to install vastly outnumbers those that are already installed and that Iran said it would now bring online by feeding them with uranium feedstock, which the IAEA verified it had yet to do.

"The Agency has determined and shared with Iran the changes required to the intensity of its inspection activities at FFEP (Fordow Fuel Enrichment Plant) following the commissioning of the cascades," the report said, referring to Iran's plan to bring eight recently installed IR-6 cascades there online.

Fordow is particularly closely watched because it is dug into a mountain and Iran is currently enriching to up to 60% there. The only other plant where it is doing that is the above-ground Pilot Fuel Enrichment Plant at Natanz.

Photo from Reuters