The diplomats told The Associated Press that the negotiations will resume on September 27, with the main focus on gaining access to a section of a military site that the UN's International Atomic Energy Agency has long tried to access.
Before the talks were suspended earlier this year, IAEA experts met Iranian negotiators 10 times over 18 months in futile efforts to start their probe of the area in question at the Parchin complex, southeast of Tehran.
With no new date announced for the resumption of broader nuclear talks between Iran and five world powers on hold, the meeting on Parchin will be the first test of centrist President Hasan Rouhani's pledge to reduce confrontation with the international community over its atomic activities.
Under former President Mahmoud Ahmadinejad, Iran blamed the IAEA for the standoff over Parchin, saying it is caused by the agency's refusal to agree on strict parameters that would govern its probe.
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It bases its suspicions of nuclear-weapons research and development by Iran on its own research and intelligence from the US, Israel and other Iran critics.
IAEA chief Yukiya Amano told reporters earlier this year he was concerned about satellite images showing asphalt work, soil removal, and "possible dismantling of infrastructures" at Parchin.
Iran says such activities are part of regular construction that has nothing to do with alleged attempts to cleanse the area of evidence.
The two Vienna-based diplomats are experts on nuclear issues. They demanded anonymity because they were not authorised to divulge the date of the meeting before official announcements by the IAEA or Iran.
They spoke just hours ahead of the expected release of the latest IAEA report documenting advances of Iran's nuclear program.