TEHRAN (Reuters) - Iran said on Sunday it was preparing to remove U.N. seals at some nuclear research and development sites, despite strong Western opposition to its decision to resume atomic work halted more than two years ago. It would be the second time in five months that Iran, which the West suspects is bent on building atomic bombs but which insists its nuclear program is peaceful, lifted some seals put in place by the International Atomic Energy Agency (IAEA). European union" and U.S. officials have said the move, which follows Iran's resumption of uranium processing at its Isfahan plant in August, will jeopardize efforts to find a diplomatic solution to Iran's nuclear ambitions and heighten calls to refer Tehran to the U.N. Security Council for possible sanctions. "We will remove the seals and we have announced that we are ready to start research from tomorrow," Foreign Ministry spokesman Hamid Reza Asefi told a weekly news conference. "It depends on the IAEA to announce its readiness as this will take place under the agency's supervision," he added. IAEA spokeswoman Melissa Fleming said two letters the Iranians sent to the U.N. watchdog agency after it called for explanations about the new plan had not resolved key questions. "The letters contain some detail but what we need is a lot of detail to prepare our inspectors. We've asked Iran for more," Fleming said. She declined to describe what detail was needed. ALARM IN THE WEST However, she noted that IAEA chief Mohamed ElBaradei "has consistently said that this suspension is conducive" to ongoing IAEA probes into the nature of Iranian nuclear work, which Tehran hid from U.N. inspectors for almost 20 years, raising alarm in the West. A resumption of atomic fuel research and development (R&D) would mean that all of Iran's nuclear program, much of which was put on hold as part of negotiations with the EU that started in late 2003, was active once again apart from the enrichment of uranium at its unfinished Natanz plant. Uranium enrichment is the most sensitive part of the nuclear fuel cycle since it can be used to produce bomb-grade material as well as fuel for civilian nuclear reactors. Iran has not publicly disclosed what activities it plans to resume on Monday. Diplomats and analysts say atomic research and development could involve some laboratory tests of uranium enrichment and assembly of centrifuge enrichment machines. "R&D activities will be under the IAEA's supervision and there is nothing to be worried about," Asefi said. However, diplomats close to the IAEA said ElBaradei had warned Iranian envoys that the R&D revival undermined attempts to resolve Iran's stand-off with the West diplomatically. "If Iran unilaterally breaks the seals, no one could depict the IAEA as being handmaiden to this act, endorsing it," one diplomat told Reuters. The diplomat said the move would prompt a report to the IAEA's 35-nation board of governors. "The members are really anxious to know what is really going on with this R&D. Their reaction will determine whether we go to an emergency board meeting or not." ElBaradei told Sky Television in an interview to be aired on Monday that the world was "running out of patience with Iran." "VERY WORRYING" Austrian Foreign Minister Ursula Plassnik, whose country has just taken over the European union" presidency, told visiting European journalists Iran was "a very worrying situation indeed." She said the EU had made it clear to Iran that, far from increasing confidence in the peaceful intentions of its nuclear program, the announced decision to resume nuclear research and development was "the wrong step in the wrong direction and is a cause of very serious concern." The next regular IAEA board session is set for March 6. Since Iran declared the R&D moratorium over, Western diplomats have privately mooted an emergency meeting within weeks. Tension in the crisis has been fanned by denunciations of Israel by Iranian President Mahmoud Ahmadinejad as a "tumor" that should be "wiped off the earth," and his dismissal of the Holocaust as "a myth." Washington and the EU want Iran to agree to a proposal, put forward by Moscow, that Iran transfer all its uranium-enrichment activities to a joint venture in Russia. Russian and Iranian officials met in Tehran at the weekend to discuss the plan but Iran has made it clear it will only consider ideas that allow it to carry out enrichment on its own soil.