The UN nuclear watchdog appears to have failed in talks with Iran this week to substantively advance a dragging investigation into suspected atomic bomb research by the country.
Western officials say Iran must improve cooperation with UN nuclear inspectors if it wants to reach a broader diplomatic deal with world powers to resolve a protracted nuclear dispute and phase out crippling financial sanctions on the oil producer.
The International Atomic Energy Agency said in a statement after the October 7-8 meeting in Tehran that discussions would continue. But it did not announce a date for the next round of talks focused on IAEA concerns that Iran had initially been supposed to address by an agreed August 25 deadline.
Meanwhile, an Iranian official said the talks were "constructive" and "direct."
"During these two days, we discussed all bilateral issues. Specifically, how to apply the measures already decided upon and the future of the discussions," said the Iranian Ambassadeur to the IAEA, Reza Najafi, according to Iranian state television.
Iran denies Western allegations that it is seeking to develop the capability to produce nuclear weapons, saying its atomic activities are aimed at generating electricity only.
Early last month, the IAEA said Iran had failed to answer questions by the August 25 target date about alleged research activities into explosives testing and neutron calculations, which could be applicable to any attempt to make nuclear bombs.
In a letter to the IAEA, Najafi has put the delay down to the "complexity" of the issues and said allegations of nuclear-orientated experiments lacked credibility and any solid proof.
In this week's talks, "the two sides held discussions in relation to the implementation of the two practical measures relating to the initiation of high explosives and to neutron transport calculations," the IAEA statement said. "The agency and Iran will continue discussions on these measures."
The IAEA gave no further detail. But its statement suggested strongly that the Islamic Republic had still not fully implemented the steps it had agreed to carry out by late August, answering questions about what the UN agency calls the possible military dimensions of Tehran's nuclear program.
It also said Iran had not offered to carry out new steps to comply with the investigation, more than a month after the IAEA asked it to do so. "Iran did not propose any new measures during the meetings in Tehran. Iran and the agency agreed to meet again, at a date to be announced," the IAEA said.
Tehran's envoy to the Vienna-based UN agency, Reza Najafi, said the discussions had been "very constructive", according to Iran's ISNA news agency, which did not elaborate.
The Vienna-based IAEA has for years been trying to get to the bottom of Western intelligence reports suggesting that Iran has worked on designing a nuclear warhead.
Iran has denounced the intelligence as fabricated, but has promised to work with the IAEA since last year when Hassan Rouhani, seen as a pragmatist, became president on a platform to overcome his country's international isolation.
US member of IAEA refused entry to Iran
Last month, the IAEA said Iran denied a visa for one member of its delegation that visited Tehran on August 31.
It was the third time the person had been unable to obtain an entry permit, the Vienna-based IAEA said. It did not reveal the official's nationality or expertise.
But diplomatic sources, who spoke on condition of anonymity due to the sensitivity of the issue, said they believed he was a US national and an atomic arms expert. The IAEA declined to comment on Thursday.
It is important, the UN agency said in a September 5 report on Iran's nuclear program, that "any staff member identified by the agency with the requisite expertise is able to participate in the agency's technical activities".
In a statement distributed to IAEA member states this week, Iran dismissed the criticism of its refusal to let one IAEA expert into the country, saying it had a sovereign right to decide who to admit onto its territory.
But its failure to issue a visa to an IAEA official may deepen longstanding Western suspicions that it is stonewalling the UN agency's investigation.
Iran and the United States have not had diplomatic ties since shortly after the 1979 Islamic revolution that ousted the US-backed shah, but they are now engaged in multilateral negotiations to try to end their decade-old nuclear dispute.
IAEA member states have the right to deny access to individual inspectors proposed by the UN agency, and Iran has for several years blocked staff from some Western nations, including the United States, to check its nuclear sites.
But the separate, high-level IAEA team in charge of the Iran inquiry - which at least on some occasions has included officials from France, the United States and Britain - has held several meetings in Tehran since early 2012.
It was unclear whether the official who was unable to take part in the August meeting was able to attend a visit by IAEA experts to the Iranian capital this week.
Iran said in its statement that it had provided visas on time to three new members of the IAEA team in recent months.
Western officials say Iran needs to cooperate with the IAEA inquiry if it wants to reach a breakthrough diplomatic settlement with world powers.
AFP contributed to this report.