The International Atomic Energy Agency's (IAEA) deputy director in charge of inspections, Olli Heinonen, arrived in Tehran on Monday for a second visit this month to talk about improving cooperation, the agency said.
Mohammad Saeedi, deputy head of Iran's Atomic Energy Organization, said talks with the IAEA would continue.
"Talks in the past three days took place in a constructive and positive atmosphere. Talks were about safeguards-related issues and the cooperation between Iran and the IAEA," he said.
Diplomats in Vienna have said Heinonen was seeking clarification about intelligence reports suggesting Iran illicitly tried to design atomic bombs. Iran has said it is not the IAEA's job "to delve into those allegations".
The IAEA said in a report in May that the alleged Iranian research into nuclear warheads was a "serious concern". Its next report on Iran is due in mid-September.
The West fears Iran is trying to obtain nuclear arms under cover of a civilian program. Iran, the world's fourth-largest oil producer, insists it needs nuclear technology to generate electricity.
Tehran now faces a fourth round of U.N. sanctions for failing to respond positively to an enhanced offer of incentives from six world powers — the United States, Russia, China, Britain, France and Germany.
Iran has so far refused to freeze any expansion of its nuclear work or suspend uranium enrichment, which would start formal negotiations on the package proposed by the six powers.
Uranium enrichment can make fuel for power plants or, if the process is adjusted, material for nuclear warheads.
(Writing by Parisa Hafezi; Editing by Meg Clothier)
