Tero Varjoranta, deputy director general of the International Atomic Energy Agency, led the team which held talks Tuesday and today on two final points on which the IAEA is still seeking explanations from Iran.
The two questions focus on concerns that the Islamic republic's nuclear activities had military dimensions.
"During these two days, all the bilateral issues were discussed, in particular, how to carry out the agreed measures and the ways forward were discussed," said Iran's ambassador to the IAEA, Reza Najafi.
The Vienna-based IAEA said that the "technical meetings" did not resolve the two outstanding issues.
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"The Agency and Iran will continue discussions on these measures" at a date to be confirmed, the body added in a statement today.
The IAEA disclosed in September that Iran had failed to meet an August 25 deadline to provide information on five points meant to allay fears it was developing nuclear weapons.
Iran insists its nuclear programme is entirely peaceful.
One of the IAEA's questions centres on Iran's purported experiments with large-scale high explosives.
Satisfying the IAEA's concerns is considered crucial to a hoped for conclusion by November 24 of a comprehensive nuclear agreement with the United States and other world powers.
In a letter to the IAEA, Najafi said the delay was due to the "complexity" of the issues and that allegations of nuclear-orientated experiments lacked credibility and any solid proof.
The visit by the watchdog's delegation came after a deadly fire on Sunday at a defence ministry plant used to produce explosives in an area east of Tehran that also houses several other military sites.
The base lies at the centre of allegations of past Iranian research into sophisticated explosives that can be used to detonate a nuclear warhead.
The Institute for Science and International Security, a US research centre, said the blast could have hit a site at the south of the Parchin complex.