PITTSBURGH, Pennsylvania — US President Barack Obama accused Iran Friday of secretly building a second uranium enrichment plant inside a mountain south of Tehran.

Obama leveled the charge before the start of a G-20 summit of the world's major economies in Pittsburgh, Pennsylvania.

The New York Times, which broke the story on its website, said the secret uranium enrichment facility was being built inside a mountain near the holy city of Qom, 100 miles (160 kilometers) south of Tehran.

Obama, British Prime Minister Gordon Brown, and French President Nicolas Sarkozy were to demand, before the start of the summit, an immediate inspection of the site by the International Atomic Energy Agency (IAEA).

In Paris the French foreign ministry, which said the statement would be made at 8:30 am (1230 GMT), called the Iranian move "a new serious violation of UN Security Council and IAEA resolutions" which "strengthens our suspicions."

In Vienna, where it has its headquarters, the IAEA said Iran had informed it on September 21 that it was building "a new pilot fuel enrichment plant."

"Iran assured the agency in the letter that 'further complementary information will be provided in an appropriate and due time'," IAEA spokesman Marc Vidricaire said.

"In response, the IAEA has requested Iran to provide specific information and access to the facility as soon as possible. This will allow the agency to assess safeguards verification requirements for the facility."

Although the facility is not complete, US officials told the Times that they believe it was designed to hold about 3,000 centrifuges, which are used to enrich uranium.

They said the facility could be in operation next year.

"They have cheated three times," a senior administration official with access to the intelligence was quoted as saying of the Iranians. "And they have now been caught three times."

Revelations by an Iranian dissident group led to the discovery of the underground enrichment plant at Natanz in 2002.

Two years ago US intelligence developed evidence that Iran had secretly tried to design a nuclear weapon, but Tehran was believed to have halted it in 2003.

The Times said the United States has been tracking the secret site for years, but decided to go public after Iran learned that its existence had been discovered by Western intelligence.

It said senior officials from several countries were pulled aside at the United Nations and at the Pittsburgh summit for briefings on the intelligence and to plot strategy for talks scheduled with Iran October 1.

The five permament members of the UN Security Council -- the United States, Russia, China, France and Britain, plus Germany -- will be represented in the talks, the first direct ones between the United States and Iran in 30 years.

At the UN General Assembly this week, Iranian President Mahmoud Ahmadinejad offered to let the country's nuclear experts meet with their western counterparts for the first time to allay their fears about Iran's nuclear program.

But he made no mention of the second uranium enrichment program alluded to in the September 21 letter to the IAEA.

World powers stepped up the pressure on Iran over its nuclear program with even Russia's President Dmitry Medvedev warning Tehran that sanctions may be "inevitable."

Obama urged world leaders on Wednesday to hold Iran -- as well as North Korea -- to account, warning that their nuclear programs threatened to take the world down a "dangerous slope."

Sarkozy also warned Iran against "making a tragic mistake" by assuming the international community will stand idly by while Tehran pursues what he called a military nuclear program.

Iran says its uranium enrichment program is for peaceful nuclear energy, denying charges it is seeking to build a nuclear bomb.

This video is from CNN's Newsroom, broadcast Sept. 25, 2009.

Download video via RawReplay.com

(with AFP)