"We were able to make progress," Herman Nackaerts, deputy director general of the International Atomic Energy Agency (IAEA), told reporters at Vienna airport after Thursday's discussions in Tehran.

More talks are due with Iran on Jan. 16.

"We expect to finalise the structured approach and start implementing it then shortly after that," he said, referring to a framework agreement that would allow the IAEA to resume its long-stalled investigation into suspected atomic bomb research in Iran.

"We had good meetings," Nackaerts added.

The comments were in line with those made by Iran's ambassador to the IAEA, Ali Asghar Soltanieh, to Iranian media after the one-day meeting in Tehran. Iranian media also said a new meeting would take place in the capital on Jan. 16.

Iran, one of the world's largest oil producers, denies Western allegations it is seeking to develop the means and technologies needed to assemble nuclear weapons.

Its economy is struggling with the burden of increasingly tough Western sanctions.