An Iranian opposition group says the Iranian government is building a secret underground military nuclear facility near its existing complex at Natanz in the central part of the country.

The opposition National Council of Resistance of Iran made the assertion at a news conference in Paris Thursday. The claim cannot be independently verified, and the group did not provide any evidence.

The group said its information came from sources within Iran, and indicates that the underground facility is five kilometers from the Natanz complex and will be operational in six months.

The United States and its allies accuse Tehran of trying to build a nuclear weapon and want to impose tougher international sanctions against Iran.

Iranian President Mahmoud Ahmadinejad said in his United Nations speech on Tuesday that Tehran's nuclear program is peaceful and transparent.

France said Thursday it does not believe him.

The spokesman for President Nicolas Sarkozy said Paris has some very strong clues indicating that Iran's nuclear program also has military goals.

The National Council of Resistance of Iran is the political arm of the People's Mujahedin of Iran, which the United States and European Union consider to be a terrorist group.

The group five years ago disclosed information about two hidden nuclear sites, including the one at Natanz, helping uncover Iran's nuclear program. However, the group has made other claims in the past that have not been verified.

Some information for this report was provided by AFP and AP.