Amid growing Israeli concerns that diplomatic efforts to stop Iran from obtaining nuclear power have failed, new satellite imagery released by a US think tank on Sunday indicated that the Islamic republic has expanded one of its uranium conversion sites and reinforced another in preparation for an aerial bombing attack. The images showed the construction of a third tunnel entrance near the uranium conversion facility in Esfahan. Mounds of earth could be seen next to the new entrance, suggesting recent excavations. In February 2005, the Institute For Science and International Security (ISIS) published satellite imagery of the construction of a tunnel facility with only two entrances. "This new entrance is indicative of a new underground facility or further expansion of the existing one," said ISIS, led by ex-UN arms inspector David Albright. While Israel officially continues to back diplomatic efforts to stop Iran's race to the bomb, the IDF and particularly the IAF, have been working on assault plans for an attack against the Iranian nuclear sites. With numerous sites spread throughout the country, the attack, officers have admitted, would be difficult although feasible. In a recent interview, a high-ranking air force officer told The Jerusalem Post that the IAF would be able to overcome Iranian air defenses including the country's relatively primitive air force. According to foreign media reports, Israel has already put an F-15 squadron on standby in preparation for a military offensive against Iran. While Israel is preparing for the possibility that military action might be the only way to stop Iran's nuclear program, officials said they preferred that America carried out the attack. "We wouldn't mind using our F-15 jets," one officer recently said, "but only if an American pilot was sitting inside." Earlier in the month, the New Yorker reported that the US was considering knocking out subterranean Iranian nuclear sites with tactical atomic bombs. The Iranian threat, an Israeli official said Sunday, was global and not just restricted to Israel. "The whole world needs to be concerned with the Iranian developments," the official said. "And the whole world needs to join forces to stop them." The Iranians, according to the images released with the ISIS report, have also recently made progress in construction at the Natanz site. The four satellite images taken between 2002 and January 2006 showed Natanz's two subterranean cascade halls being buried by successive layers of earth, apparent concrete slabs, more earth and other materials, showing a clear attempt to reinforce the hall from potential aerial bombing attacks. The roofs of the halls now appear to be eight meters underground, ISIS said. The new revelations came less than a week after President Mahmoud Ahmadinejad announced that Iran had passed one of the major hurdles in its race to obtain nuclear power and had, for the first time, successfully enriched uranium. Over the weekend, a high-ranking IDF officer told the Post that Iran, if allowed to continue enriching uranium, could have nuclear weapons already within two-and-a-half years. While only 164 centrifuges were used to enrich the uranium to 3.5 percent last week, it was only a matter of time, the officer said, before Iran obtained technology allowing for the operation of thousands of centrifuges over a period of several months which could produce highly enriched uranium needed for a nuclear bomb. "Once they succeeded in enriching uranium at 3.5% there is nothing really technologically stopping them from enriching at 90%," the officer asserted.