His trip to the Russian exclave, which is wedged between Poland and Lithuania, came a week after he visited the embattled plant, where he said he was working on a safety plan that would suit both Kyiv and Moscow.

The Russian forces took control of the six-reactor plant in southern Ukraine in March last year, days after Russian President Vladimir Putin sent troops across the border.

There have been persistent fears over the safety of the plant, which is Europe's largest atomic power station.

"I met high level officials from several Russian agencies in Kaliningrad," Grossi said on Twitter.

"I continue my efforts to protect the Zaporizhzhia Nuclear Power Plant," he said, adding that this was "in everyone's interest."

He did not provide further details.

The head of Russia's nuclear agency Rosatom, Alexei Likhachev, was among the officials Grossi met.

Likhachev had informed Grossi of "the steps that are being taken by the Russian side to ensure the safe operation" of the plant, Rosatom said in a statement.

The statement added that the Russian side was "ready to work on" initiatives put forward by Grossi.

On a visit to the plant last week, Grossi said he was "trying to prepare and propose realistic measures that will be approved by all parties."

"We must avoid catastrophe," he warned and expressed hope that Russia and Ukraine would agree on safety principles.

Kyiv and Moscow have accused each other of shelling the plant, increasing fears of a disaster.

The United Nations has called for a demilitarised zone around the site.