Kayhan daily, which is close to Iran's ruling clerics, said on Sunday that Tehran has begun injecting uranium gas into sophisticated centrifuges at the Fordo facility near the holy city of Qom.

"Kayhan received reports yesterday that showed Iran has begun uranium enrichment at the Fordo facility amid heightened foreign enemy threats," the paper said in a front-page report. Kayhan's manager is a representative of Iran's Supreme Leader Ayatollah Ali Khamenei.

But Iran's nuclear chief Fereidoun Abbasi said late Saturday that his country will "soon" begin enrichment at Fordo. It was impossible to immediately reconcile the two reports.

Iran has a major uranium enrichment facility in Natanz in central Iran where nearly 8,000 centrifuges are operating. Tehran began enrichment at Natanz in April 2006.

The Fordo centrifuges however are reportedly more efficient, and the site better shielded from aerial attack.

Built next to a military complex, Fordo was long kept secret and was only acknowledged by Iran after it was identified by Western intelligence agencies in September 2009.

Uranium enrichment lies at the heart of Iran's dispute with the West. The technology that can be used to produce nuclear fuel, but also materials for atomic bombs.

The U.S. and its allies fear Iran's ability to make its own nuclear fuel will eventually lead to atomic weapons, because the technology offers a possible pathway to weapons-grade nuclear material.

Iran says it only seeks reactors for energy and research, but refuses to halt its uranium enrichment activities. It says it needs to keep the enrichment program to produce fuel for future nuclear reactors and medical radioisotopes needed for cancer patients.