The IAEA talks are distinct from Iran's meetings with world powers, but both diplomatic tracks centre on suspicions that Iran may be seeking the capability to assemble nuclear bombs behind the facade of a civilian atomic energy programme.
Israel and the United States have threatened possible pre-emptive strikes on Iran if diplomacy fails. Iran says its nuclear programme is a peaceful bid to generate electricity, and not aimed at building weapons.
Herman Nackaerts, IAEA deputy director general, said the discussions, at Iran's diplomatic mission in Vienna, had been "very constructive" but gave no details. At the next meeting on October 28, Iran and the IAEA would "start substantial discussions on the way forward to resolve all outstanding issues," he said.
That would be almost two weeks after Iran meets the six world powers again, in Geneva on October 15-16, as part of what European Union foreign policy chief Catherine Ashton called an "ambitious timetable" to address Western concerns.