The chief of the UN nuclear watchdog says the head of the Russian-occupied Zaporizhzhia nuclear power plant has been released.

International Atomic Energy Agency Director General Rafael Grossi made the announcement on Twitter on Monday.

Grossi wrote that he has received confirmation that Ihor Murashov, director general of the Zaporizhzhia plant, "has returned to his family safely."

Ukraine's state nuclear power company Energoatom said in a social media post that the director general came back to the plant on Monday following his release. The firm added that the IAEA chief played a major role in securing his release.

On Saturday, Energoatom said Murashov was detained by Russians on Friday while on his way from the plant to a nearby town.

The IAEA called the detention a "source of grave concern" and said it would get in touch with relevant authorities.