IAEA deputy director Rafael Grossi, one of the top officials in negotiations over Iran's nuclear drive, has announced his resignation, the UN nuclear watchdog said Sunday.

"I can confirm Assistant Director General Rafael Grossi has submitted his resignation from the IAEA," an International Atomic Energy Agency spokeswoman told AFP.

"The timing of his departure will be defined very soon," she added.

No reasons were given for the Argentinian's resignation, which comes as chief inspector Herman Nackaerts of Belgium prepares to retire later this year.

Nackaerts and IAEA number two Grossi led fruitless talks with Iran last year over its controversial nuclear programme, which Tehran insists is peaceful, while the West suspects it is a cover for building an atomic bomb.

During a series of meetings in Vienna and Tehran, the two tried but failed to get Iran to allow IAEA inspectors greater access to its nuclear programme.

Tero Varjoranto of Finland is due to take over from Nackaerts as chief inspector in October.

IAEA chief Yukiya Amano was meanwhile elected last month to a second four-year term, which will start in December.