Atomic sites have been a key concern throughout the nearly one year-long conflict, with attacks around several facilities raising fears of a nuclear incident.

Grossi visited Ukraine last month to dispatch International Atomic Energy Agency (IAEA) teams at several nuclear facilities, building on its mission at the Russian-controlled Zaporizhzhia plant near the frontline.

"The IAEA Director General is flying to Moscow today," Deputy Foreign Minister Sergei Ryabkov told the state-run RIA Novosti news agency.

"His trip is important. We have been discussing parameters for a nuclear and security protection zone for a long time," he added.

The talks are "not easy," Ryabkov said, according to RIA Novosti.

"We understand that the agency and its leadership are under external pressure," he added.

Kyiv and Moscow have repeatedly blamed each other for shelling the Zaporizhzhia facility, Europe's largest nuclear plant.

Russia has controlled the plant since March last year and claims to have annexed the surrounding Zaporizhzhia region.