Nuclear experts from the International Atomic Energy Agency (IAEA) will hold talks Tuesday in Tehran to try and resolve outstanding issues regarding Iran's disputed atomic programme.
The official IRNA news agency said the visitors were expected in the capital on Monday night ahead of talks with Iranian officials.
"The visit of Tero Varjoranta, deputy director general of the IAEA, and a delegation will continue discussions to finalise the last two points" on which an explanation from Iran is sought, it said.
Those two questions -- to the Atomic Energy Organisation of Iran -- focus on concerns that the Islamic republic's nuclear activities had military dimensions.
The Vienna-based 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.
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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.
Under an agreement reached in November 2013 with the IAEA, Iran has already responded to 16 of the 18 issues the agency identified as relevant to Iran's nuclear activities.
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.
A large majority of US House of Representatives members wrote to Secretary of State John Kerry last week accusing Iran of its "refusal" to work with the UN watchdog.
"The only reasonable conclusion for its stonewalling of international investigators is that Tehran does indeed have much to hide," the US lawmakers said.