Iran said on Wednesday that talks on its controversial nuclear drive with top UN atomic watchdog official Olli Heinonen were "positive" and would continue.

"The negotiations held over the past three days were positive and will continue," said the deputy chief of Iran's atomic energy organisation, Mohammad Saeedi.

"The two sides have agreed to continue these discussions," he added, without providing any details on the nature of the talks.

International Atomic Energy Agency (IAEA) deputy chief Heinonen arrived in Tehran on Monday for a second round of talks with Iranian officials this month.

According to the official news agency IRNA he was expected to leave Iran late Wednesday.

Ali Asghar Soltanieh, Iran's representative at the IAEA, meanwhile, said that "negotiations... on technical cooperation between Iran and the IAEA will continue."

Heinonen has made a number of visits as part of the agency's longstanding efforts to ensure there is no military dimension to the nuclear drive, which some Western states fear could be a cover for a secret weapons project.

Iran insists that its nuclear programme is aimed solely at generating energy for its growing population.

Heinonen's latest trip -- which comes ahead of a new IAEA report on Iran expected in September -- follows on August 7 talks in Tehran that Iranian officials had also described as "positive" but without giving details.

The visit comes as Iran risks a possible fourth round of UN sanctions after it failed to give a clear response to an incentives package offered by six major world powers in return for halting uranium enrichment, a process which makes nuclear fuel but also the core of an atomic bomb.