At a news conference in the Iranian city of Isfahan, Grossi said he had proposed in talks with Iranian officials that they "focus on the very concrete, very practical and tangible measures that can be implemented in order to accelerate" cooperation.

Grossi held discussions with senior Iranian officials including the Atomic Energy Organization of Iran chief Mohammad Eslami.

The IAEA director general said a March 2023 agreement with Iran was "still valid" but required more "substance" to be added.

The agreement was reached during Grossi's last visit to Iran and outlined basic cooperation measuring including on safeguards and monitoring.

The IAEA chief said, however, that there had been a "slowdown" in its implementation.

Iran has suspended its compliance with caps on nuclear activities set by a landmark 2015 deal with major powers after the United States in 2018 unilaterally withdrew from the agreement and reimposed sweeping sanctions.

Tensions between Iran and the IAEA have repeatedly flared since the deal fell apart, and EU-mediated efforts have so far failed both to bring Washington back on board and to get Tehran to again comply with the terms of the accord.

The agency has in recent months criticised Iran for lack of cooperation on issues including the expansion of its nuclear work, the barring of inspectors and deactivating the agency's monitoring devices at its nuclear facilities.

In February, it said in a confidential report seen by AFP that Iran's estimated stockpile of enriched uranium had reached 27 times the limit set out in the 2015 accord.

Last year, Iran slowed the pace of its uranium enrichment, which was seen as a goodwill gesture while informal talks began with the United States.

But Iran then accelerated the production of 60 percent enriched uranium in late 2023, according to the IAEA.

Enrichment levels of around 90 percent are required for military use.

During the conference, Eslami said that talks with Grossi were "constructive," and agreed that the 2023 agreement was a "good basis for interactions" between Iran and the agency.