The head of the International Atomic Energy Agency has expressed concern after Ukraine's state-owned Energoatom announced that Russia has detained the director general of the Zaporizhzhia nuclear plant.

IAEA Director General Rafael Grossi said in a statement on Saturday, "Such a detention of any member of the plant staff would be a source of grave concern in itself, but also for its psychological impact and pressure on the rest of the staff -- which is detrimental to nuclear safety and security."

Grossi noted that the detained director general, Ihor Murashov, activates and leads the response to any on-site nuclear emergency.

He said, "His absence from duty in this way also has an immediate and serious impact on decision-making in ensuring the safety and security of the plant."

Grossi called for the swift release of the director general.

The Zaporizhzhia plant, which has been controlled by Russian forces since the early days of the invasion, has temporarily lost external power due to heavy shelling.

The IAEA says Grossi is continuing consultations and other efforts aimed at agreeing and implementing a nuclear safety and security zone around the plant. It says he is expected to travel to Ukraine and Russia in the coming week.