Rafael Grossi said the IAEA and Iran "did have a number of important matters that we needed... to resolve", but that they had now "decided to try a practical, pragmatic approach" to overcome them.

He was speaking during a joint news conference with Mohammed Eslami, head of the Atomic Energy Organization of Iran, after talks seen as crucial to reviving the 2015 Iran nuclear deal.

Eslami said the two sides had come to the "conclusion that some documents which need to be exchanged between the IAEA and the Iranian organisation should be exchanged" by May 22.

Ongoing talks in the Austrian capital to restore the agreement involve Iran as well as Britain, China, France, Germany and Russia directly, and the United States indirectly.

The 2015 agreement gave Iran sanctions relief in return for curbs on its nuclear programme, but the US unilaterally withdrew from it in 2018 under then-president Donald Trump who reimposed crippling economic sanctions.

That prompted Iran to begin rolling back on its own commitments from 2019.

Iran has also restricted some inspections by the IAEA, which wants Tehran to resolve questions surrounding the previous presence of nuclear material at undeclared sites.

The Islamic republic has said the completion of the probe is necessary to clinch a nuclear deal.

Grossi said the two issues were "closely interrelated".

"While these processes in a way are parallel... one cannot ignore the other," said the IAEA director general.

"So this is why it's important to have this understanding between us today, which is an understanding to work together, to work very intensively," he added.