Israeli officials believe the revelation of a hitherto-hidden uranium enrichment facility near the Iranian holy city of Qom will spur the international community to act more forcefully to stop the Islamic republic from developing nuclear weapons, The Jerusalem Post has learned. "The free world has reached the last opportunity for engagement with Iran. We believe many Western countries now see that the Iranian mask is slipping," a senior official told the Post on Saturday night. "But we don't yet know if Russia and China understand this," the official added, citing two countries that have disagreed with Israel and many Western states on the need for further sanctions. Later on Saturday night, a senior Obama administration official revealed that the US and its five partners - France, Russia, the UK, Germany and China - plan to tell Teheran at a meeting in Geneva on Thursday that it must provide "unfettered access" to its previously secret Qom enrichment facility within weeks. The six major powers also will present a so-called transparency package covering all of Iran's nuclear activities, the official said. The official spoke on condition of anonymity in order to discuss plans that are not yet ready to be announced. The six countries will demand full access for the International Atomic Energy Agency to any and every site, notebooks, computers and documents related to nuclear development, and all scientists. They will demand that Iran prove to the increasingly skeptical group that its intentions with its various sites are peaceful and energy-related, as Iran claims, and not for weapons development, as the West believes. Meanwhile in Israel, a source in the Prime Minister's Office said "it was not a surprise to the prime minister" that Iran had an additional nuclear facility. The source said that Prime Minister Binyamin Netanyahu discussed Iran and other issues over the weekend with top congressmen, including House Speaker Nancy Pelosi (D-California); Senate Minority Leader Mitch McConnell (R-Kentucky) and veteran Sen. Daniel Inouye (D-Hawaii). "If not now then when?" the official quoted Netanyahu as saying. While Israeli diplomats have been told not to comment on the revelations before they are studied in detail, Foreign Minister Avigdor Lieberman gave an early reaction to the news earlier on Saturday that seemed to echo the American president's reaction. "This ends the dispute over whether Iran is developing military nuclear power or not, and therefore world powers need to draw conclusions," Lieberman told Israel Radio. "Without a doubt it is a reactor for military purposes, not peaceful ones," he said. He urged immediate action by the international community to "overthrow the mad regime of Teheran," according to AFP. Lieberman said that in his meetings with Arab foreign ministers at the UN General Assembly last week, they expressed alarm over Iran's nuclear program. "Nobody is worried about the Palestinian problem; everybody in the Muslim and Arab world - and first and foremost in the Gulf states - is worried about the Iranian problem," he said. Iran kept the facility, located underground in arid, mountainous terrain 160 km. southwest of Teheran, hidden from the UN's International Atomic Energy Agency, revealing it only over the weekend. The site is capable of housing some 3,000 centrifuges, according to Western intelligence sources, far less than the 8,000 currently housed at the enrichment facility at Natanz, the only other facility currently known to be operating in Iran. According to Western officials, and acknowledged by Iran, the disclosure came after Western intelligence agencies had learned of the facility and Western leaders planned to reveal it to the world. Iran's vice president, Ali Akbar Salehi, who also heads the country's Atomic Energy Organization, said on Saturday that by reporting the existence of the site voluntarily to the IAEA, Iran "preempted a conspiracy" by the US and its allies, who had been hoping to reveal the site as evidence that Iran was developing its nuclear program in secret. Declaring that the new site "is inconsistent with a peaceful [nuclear] program," US President Barack Obama on Friday accused Teheran of "breaking rules that all nations must follow." He called the newly revealed site "a direct challenge to the basic foundation of the nonproliferation regime." Salehi told state television on Saturday that Iran would allow the IAEA to inspect the facility, though he did not give a timeline. Israeli government agencies will be studying the new information, which according to reports has been known for some time by intelligence agencies, and for about three years by the US. However, due to Yom Kippur, the issue won't be brought before the full cabinet until the ministers' next meeting on Wednesday. Meanwhile, US Jewish groups argued over the weekend that the revelations made a case for the immediate implementation of new sanctions aimed at stopping the Iranian nuclear program. "The time is now, not months from now, to determine the most effective and impactful sanctions and implement them," leaders of the Conference of Presidents of Major American Jewish Organizations said in a statement. "Should the UN Security Council not be able to muster the votes necessary, then Europe, the US and other nations should act outside of the framework of that body," Alan Solow and Malcolm Hoenlein, the Conference's chairman and executive vice chairman, respectively, said in Friday's statement. The American Jewish Committee said it had "grave concerns" over the revelations, which amounted to "further incontrovertible proof that any assurances from Iranian leaders about the nature and scope of their nuclear program are worthless." "Whether they are denying the Holocaust or trying to fool us over their nuclear ambitions, it's clear that lying is what Iran's leaders do best," the group's executive director David Harris said in a statement. "The discovery of this second facility fits perfectly into the web of deceit which Iran has woven around its nuclear program. Let's recall that the regime also tried to conceal the Natanz facility from the outside world. We are compelled to ask: What else are they hiding?" Hilary Leila Krieger, Gil Hoffman and AP contributed to this report.