Rafael Grossi was expected at Europe's largest nuclear power plant on Wednesday to assess impacts to the site's safety after the destruction of the Kakhovka dam.

The breach of the dam, which formed a reservoir to provide cooling water for the plant, has exacerbated ongoing concerns over the facility.

Kyiv did not confirm the delay and the International Atomic Energy Agency (IAEA) did not confirm or deny the Russian reports.

"The mission is being postponed by a day," Russian state news agency TASS quoted a nuclear official as saying, without giving a reason.

The head of Russian-installed authorities in the Zaporizhzhia region, Yevgeny Balitsky, also said the trip was delayed.

"We will wait for Grossi at the Zaporizhzhia nuclear power plant on June 15, the visit is delayed by a day," he was quoted by the Interfax news agency as saying.

According to a Western diplomatic source contacted by AFP, Grossi's visit has been delayed "by a few hours, but not cancelled".

His mission to the plant should take place "soon", the source said Wednesday, adding that "security checks are currently being conducted, in view of the general situation in the region."

Grossi has visited the plant twice since it has been occupied by Russia.

Its safety has been a concern since Russian forces seized it over a year ago.