A team of UN inspectors prepared Sunday for their first look inside a formerly secret - though still unfinished - uranium enrichment facility that has raised Western suspicions about the extent of Iran's nuclear program. The inspection tour will provide the world's first independent details of the heavily protected site, carved into a mountainside near the holy city of Qom south of Teheran. It also coincides with the countdown to Iran's expected decision on whether to accept a UN-brokered plan to process its nuclear fuel abroad. Iran promised to respond later this week on the proposal, which seeks to ease international worries that Iranian labs could push the uranium enrichment to higher levels for weapons-grade material. Iran claims it only seeks peaceful reactors for research and energy. Although Iran has not given its official answer on the proposed nuclear deal - discussed last week after talks in Vienna with the United States, France and Russia - there are increasing doubts that Iran's leadership will come on board. On Saturday, Parliament Speaker Ali Larijani claimed the West was trying to "cheat" Iran under the deal that would ship most of Iran's uranium to Russia for reactor-ready enrichment. Larijani, the country's former nuclear negotiator, said Iran prefers to buy the nuclear fuel it needs for a reactor under construction that makes medical isotopes. He did not specifically address the fuel needs for Iran's planned Russian-built full-scale reactor, but Russia is required to provide fuel as part of agreement to build it for Iran in the southern city of Bushehr. The reactor is nearly operational. Rejection of the UN deal would force the United States and its allies to either return to talks or step up demands for greater economic sanctions. The inspection of the newly revealed facility - known as Fordo after a village believed to have the largest percentage of fighters killed in the 1980-88 war with Iraq - is Iran's second enrichment site and raised international suspicion over the extent and aim of Teheran's nuclear program. But Iran says that by reporting the existence of the site voluntarily to the UN's nuclear watchdog, it "pre-empted a conspiracy" against Teheran by the US and its allies who were hoping to present the site as evidence that Iran was developing its nuclear program in secret. State television showed the arrivals of inspectors, but officials have not given a schedule for the visit to the facility or whether it would occur Sunday or later. The delegation from the International Atomic Energy Agency is led by Herman Nackaerts, director of IAEA's division of operations department of safeguards. The inspectors are expected to stay three days in Iran. The Fordo uranium enrichment site, about 30 kilometers north of Qom, is heavily guarded by military installations including missile silos and anti-aircraft batteries, Iranian officials said last month. Iran said the facility won't be operational for another 18 months. The small-scale site is meant to house no more than 3,000 centrifuges - much less than the estimated 8,000 machines at Natanz, Iran's known industrial-scale enrichment facility. Still, the enriching machines in Qom facility will produce nuclear fuel, which could possibly be further enriched into material for atomic warheads. Iran said it has built the facility inside a mountain next to a military site to protect its nuclear activities in case of an attack by the US or Israel. A recent satellite image provided by DigitalGlobe and GeoEye shows a well-fortified facility built into a mountain about 30 kilometers northeast of Qom, with ventilation shafts and a nearby surface-to-air missile site, according to defense consultancy IHS Jane's, which did the analysis of the imagery. The image was taken in September. GlobalSecurity.org analyzed images from 2005 and January 2009 when the site was in an earlier phase of construction and believes the facility is not underground but was instead cut into a mountain. It is constructed of heavily reinforced concrete and is about the size of a football field - large enough to house 3,000 centrifuges used to refine uranium. Iranian officials said the site was selected after a careful study by experts. They said it was formerly an ammunition depot. On Saturday, US President Barack Obama called French President Nicolas Sarkozy and Russian President Dmitry Medvedev to reaffirm their commitment to a UN-backed plan that would ship most of Iran's uranium abroad for enrichment. The three presidents endorsed the proposal this week as a means of calming fears in the West that Iran is developing a nuclear weapon. Iran has not said whether it will comply, but asked for more time Friday to consider the plan. The White House said that Obama thanked Sarkozy and Medvedev for their help in addressing the issue and discussed the importance of implementing it soon.