Rafael Grossi, director general of the International Atomic Energy Agency (IAEA), told the quarterly meeting of the board of governors that his talks in Tehran were "inconclusive", despite what he had earlier described as "intense" negotations.

"We could not agree yesterday, in spite of my best efforts," Grossi told reporters on Wednesday, shortly after addressing the board meeting.

Among other officials in Tehran, he met Mohammad Eslami, the head of the Atomic Energy Organization of Iran.

He had been hoping to make progress on several points of contention between the agency and Tehran.

These include the constraints put on IAEA inspections activity earlier this year, outstanding questions over the presence of undeclared nuclear material at sites in Iran, and the treatment of IAEA staff in the country.

The talks came ahead of the scheduled resumption on Monday of negotiations between Tehran and world powers aimed at reviving the 2015 deal that gave Iran sanctions relief in return for curbs on its nuclear programme.