A high-level UN nuclear watchdog team will visit Tehran for talks in coming days, Iran said yesterday, 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 UN 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 website 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 co-operation with the IAEA if it wants to reach a broader diplomatic deal with world powers that would end a decade-old nuclear dispute and gradually end crippling financial and other sanctions on the oil producer.

Early last month, the IAEA said Iran had failed to answer questions by an agreed August 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 Rohani, seen as a pragmatist, became president last year on a platform to end the country’s international isolation.

But in a letter to US Secretary of State John Kerry released on Thursday, 354 members—four-fifths—of the US House of Representatives said they were deeply concerned about Iran’s “refusal to fully co-operate” 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.

While the powers seek to limit the size of Iran’s future nuclear programme, 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.