NEW YORK - Leaders of the United States, France and Britain accused Iran Friday of building a secret uranium-enrichment facility that could have military uses, and threatened tougher UN sanctions unless the Islamic republic suspends its nuclear programme by December. The size and configuration of this facility is inconsistent with a peaceful programme, US President Barack Obama said in a televised appearance with French President Nicolas Sarkozy and British Prime Minister Gordon Brown in Pittsburgh, where they are attending the G-20 summit. Experts say the enrichment process can produce low-enriched uranium for nuclear power plants and highly enriched uranium for nuclear bomb fuel. US intelligence officials told news media the plant was in a deeply buried underground complex in a base run by the elite Islamic Revolutionary Guard Corps. They said it was designed to hold 3,000 centrifuges, the devices used to convert uranium hexafluoride gas into low enriched or highly enriched uranium. They think it will be completed by the end of next year. With all 3,000 centrifuges running at full capacity, it would be capable of producing enough highly enriched uranium for one nuclear bomb per year, they said. UN Diplomats said it could make it harder for Russia and China to oppose tougher sanctions on Tehran should Iran refuse again to abide by UN resolutions to suspend its nuclear programme. At that meeting, Iran must be prepared to cooperate fully and comprehensively, Obama said. The Iranian government must now demonstrate through deeds its peaceful intentions or be held accountable. Sarkozy, speaking in even harsher terms than Obama did, said Iran had until December to comply with a series of UN resolutions. These require Iran to suspend its enrichment of uranium and open negotiations on a deal to ensure that its program is strictly for peaceful purposes. Everything, everything must be put on the table now, he said. We cannot allow Iranian leaders to gain time while the motors are running. Iran, apparently forewarned that US and French intelligence agencies had been monitoring the construction of the secret facility near the holy city of Qom for several years, sent a letter Monday to the UN International Atomic Energy Agency admitting the construction of a pilot plant. A senior administration official said, however, that the letter disclosed no details about the facility, including where it is or what its purpose is. Obama said that the existence of the plant underscores Irans refusal to live up to its obligations under UN resolutions and international law and represents a direct challenge to the Non-Proliferation Treaty, the cornerstone of the international system designed to halt the spread of nuclear weapons. The revelation of the secret plant and Irans confirmation appear to contradict its assertions and violate its safeguards agreement with the IAEA and UN resolutions prohibiting it from undertaking new nuclear activities. The existence of the facility appears to account for the continued charges by the United States and its allies that Iran may be secretly developing nuclear weapons. AFP and Reuters add: Iran has informed the UN atomic watchdog that it is building a second uranium enrichment plant, the IAEA said in Vienna on Friday. On September 21, Iran informed the IAEA in a letter that a new pilot fuel enrichment plant is under construction in the country, the watchdogs spokesman Marc Vidricaire said in a statement. Iran assured the agency in the letter that 'further complementary information will be provided in an appropriate and due time, 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. So far, Iran has only had one uranium enrichment plant in operation, in Natanz. The letter stated that the enrichment level would be up to 5.0 per cent, which is a low level of enrichment and not a sufficiently high to make the fissile material for an atomic bomb. Turning up the heat in the dispute over Tehrans nuclear programme, Iranian President Mahmoud Ahmadinejad said the Islamic republic was not obliged to tell the Obama Administration of every uranium enrichment plant it has, denying his country was working in secret on its nuclear programme. And he warned US President Barack Obama against making a statement pressing Tehran on the revelations that it built a second uranium enrichment plant. This does not mean we must inform Obamas Administration of every facility that we have, he told Time magazine in an interview when asked about US President Barack Obamas charge on Friday that a nuclear fuel plant Iran disclosed this week had been built secretly. We have no secrecy, we work within the framework of the IAEA, Ahmadinejad told Time in a reference to the UN nuclear watchdog. Irans nuclear chief Ali Akbar Salehi said, In a successful new step, the Islamic republic has created another semi-industrial nuclear fuel enrichment plant. The activities of this facility will be within IAEA regulations. The building of the second facility was a guarantee that the Islamic republics nuclear work will never stop, Salehi was quoted as saying by the official IRNA news agency. Russia and China were told recently of the existence of a secret Iranian uranium enrichment plant which the West suspects could be used to make a bomb, a French official said Friday in Pittsburgh. The French Foreign Ministry accused Iran of committing a serious violation of UN resolutions with the admission of a second uranium plant. This strengthens our suspicions, said foreign ministry spokeswoman Christine Fages. In Brussels, the Wests chief nuclear negotiator, Javier Solana, backed demands by the US, Britain and France for UN access to a new atomic site revealed by Iran, his spokeswoman said.