The head of the UN nuclear watchdog said Iran is operating only several hundred centrifuges at its uranium enrichment plant at Natanz, despite its claims to have activated 3,000. Mohamed ElBaradei said Thursday that Iran's nuclear program was a concern, but he discounted Tehran's claims of a major advance in uranium enrichment, a process the United Nations demands Iran suspend or else be hit by increasing sanctions. Iranian President Mahmoud Ahmadinejad announced Monday that the Natanz facility had begun "industrial-scale" production of nuclear fuel. Iran's top nuclear negotiator said workers had begun injecting uranium gas into a new array of 3,000 centrifuges, many more than the 328 centrifuges known to be operating at Natanz. Experts say that 3,000 centrifuges would be enough in theory to develop a nuclear warhead in about a year, but they doubt Iran really had that many devices successfully running.