The UN nuclear watchdog plans talks with Iran on Monday ahead of a 15 May deadline for the country to implement a series of measures that could allay concern about its nuclear programme that the West fears may have military goals.
News of the meeting came after diplomatic sources told Reuters on Friday that the International Atomic Energy Agency was seeking further clarification from Iran about one of those steps, concerning information about detonators that can help set off a nuclear device and Tehran is believed to have developed.
Iran says it has already implemented the seven steps agreed by the two sides - including access to two uranium sites - but the sources suggested the IAEA still wanted more information about the so-called Explosive Bridge Wire (EBW) detonators.
How Iran responds to questions about its development and need of this type of equipment is seen as an important test of its willingness to cooperate fully with an IAEA investigation into suspected atomic bomb research by the country.
Iran says allegations of such work are baseless, but has offered to help clear up the suspicions with the UN agency.
The diplomatic sources said Iran in late April provided an explanation about the detonators, which it says are for non-nuclear uses, and that the IAEA had asked follow-up questions.
They said the IAEA also wants to agree with Iran new measures to be taken after 15 May, hoping these will tackle other sensitive issues linked to what the agency calls the possible military dimensions to Iran's nuclear programme.
IAEA spokeswoman Gill Tudor said in an email on Sunday that the meeting would take place in Vienna but gave no detail.
"IAEA and Iranian officials will meet ... for further discussions within the Framework for Cooperation," she said, referring to a transparency pact reached in November on a step-by-step process to shed more light on Iran's atomic activity.
IRAN SAYS "INSPECTORS SATISFIED"
A senior Iranian nuclear official gave an upbeat assessment of the country's cooperation with the IAEA so far.
"Our initial impression is that the inspectors were satisfied with what they saw and the information they received," Behruz Kamalvandi told Fars News Agency, after IAEA officials last week toured the Saghand uranium mine and a linked site.
Iran and the IAEA will meet a day before the Islamic Republic and six world powers on Tuesday start, also in the Austrian capital, a new round of negotiations on a broad diplomatic settlement of the decade-old nuclear dispute.
The two sets of negotiations are separate but closely linked as both focus on fears that Iran may be covertly seeking the capability to develop nuclear weapons. Iran says its nuclear programme is a peaceful energy project only.
Western diplomats say Iran must start engaging with the IAEA's investigation and that this is central to the success of the powers' talks with Tehran aimed at a comprehensive deal by late July.
Iran wants an end to sanctions that are severely hurting its oil-dependent economy. After years of a worsening standoff with the West, the election last year of pragmatist Hassan Rouhani as Iran's president opened the way for a thaw.