Sept. 25 (Bloomberg) -- Iran has been secretly building a nuclear fuel plant with the potential to manufacture enough enriched uranium for one atomic weapon every year, a diplomat from a Group of Seven nation said.

U.S., British and French intelligence agencies have known about the construction of an underground facility since 2006, the diplomat, who declined to be identified, told reporters in Pittsburgh today. The site is the same as the one disclosed by Iran on Sept. 21 to the United Nations’ International Atomic Energy Agency.

The site’s existence prompted U.S. President Barack Obama, French President Nicolas Sarkozy and British Prime Minister Gordon Brown to today demand Iran submit to international demands to halt uranium enrichment or face new sanctions.

The diplomat said the three nations have no interest in a military response against Iran at present.

The United Nations’ International Atomic Energy Agency said in a statement it received a letter from Iran on Sept. 21 saying that a new pilot fuel-enrichment plant was under construction.

It is sited at a former Revolutionary Guard missile site on a mountain to the northeast of the city of Qum, which is near Tehran. Israel has also had knowledge of the project, the diplomat added.

Iran is some distance away from finishing work at the site, said the diplomat, who was attending talks at the G-20 summit. Evacuation and tunneling has taken place, although it is not operational yet.

Disclosure

Obama met with the leaders of China and Russia at UN meetings in New York this week, trying to persuade them to join U.S. and European governments in stepping up the threat of sanctions against Iran.

Obama told Hu Jintao of China and Dmitri Medvedev of Russia that Iran can’t be allowed to flout international rules requiring the disclosure of nuclear activities.

The plant would be big enough to house about 3,000 centrifuges, the diplomat said. That’s too big for it to be a 164-centrifuge test site as the Iranians claim and too small for a plant producing fuel for civilian power plants, which would typically house about 50,000 centrifuges, he said.

The diplomat added that Iran wouldn’t need to import technology or hire foreign assistance to finish the plant.

To contact the reporters on this story: Gonzalo Vina in London at gvina@bloomberg.net;

Last Updated: September 25, 2009 13:38 EDT