A high-level U.N. nuclear watchdog team will visit Tehran for talks in coming days, Iran said on Friday, more than a month after it missed a deadline for addressing questions about its suspected atomic bomb research. Diplomats told Reuters on Thursday that the International Atomic Energy Agency (IAEA) was expected to make a new attempt soon to advance its long-running investigation into Iran's nuclear programme and that a meeting might be held in the Iranian capital early next week. Reza Najafi, Iran's ambassador to the Vienna-based U.N. agency, said the IAEA delegation would be led by the head of its division dealing with nuclear safeguards issues, Deputy Director General Tero Varjoranta. In an apparent reference to Thursday's Reuters article, Najafi was quoted as saying on the web site of Iran's Press TV television: "It is regrettable that classified information in the agency has not been protected again." He added: "While Iran and the agency were busy planning (the meeting), the news was published by a Western media outlet ... This issue once again confirms Iran’s misgivings that spying exists in the agency." There was no immediate comment from the IAEA, which for years has been trying to investigate Western allegations that Iran has worked on designing a nuclear warhead. Iran says its nuclear programme is peaceful and that it is working with the IAEA to clear up any suspicions about it. Western officials say Iran must step up cooperation with the IAEA if it wants to reach a broader diplomatic deal with world powers that would end a decade-old nuclear dispute and financial and other sanctions on the oil producer. US LAWMAKERS " DEEPLY CONCERNED " Early last month, the IAEA said Iran had failed to answer questions by an agreed Aug. 25 deadline about two areas of the investigation into alleged research activities that could be applicable to any attempt to make nuclear bombs - explosives testing and neutron calculations. While rejecting the accusations as baseless, Iran has promised to engage with the IAEA since Hassan Rouhani, seen as a pragmatist, became president last year. But in a letter to U.S. Secretary of State John Kerry released on Thursday, 354 members -- four-fifths -- of the U.S. House of Representatives said they were deeply concerned about "refusal to fully cooperate" with the IAEA. A nuclear deal between Iran and the powers that "effectively prevents Iran from acquiring a nuclear weapons capability demands transparency on the extensive research and development work that Iran has undertaken in the past," they wrote. Rouhani's election raised hopes of a solution to the nuclear stand-off with the West after years of tension that raised fears of a new Middle East war. An interim accord was reached between Iran and six major powers -- the United States, France, Germany, Britain, China and Russia -- in Geneva last November. But they did not meet a self-imposed July target date for a long-term accord and now face a new deadline of Nov. 24. While the powers seek to limit the size of Iran's future nuclear program, and thereby extend the time it would need for any attempt to accumulate fissile material for a weapon, the IAEA is investigating alleged research and experiments in the past that could be used to make the bomb itself.