Ukraine's President Volodymyr Zelenskyy has ordered military commanders to strengthen defenses in the north after the reported arrival of Wagner Group leader Yevgeny Prigozhin in neighboring Belarus.

Zelenskyy said via social media on Friday that he took the decision in a meeting of top military leaders including Commander-in-Chief Valerii Zaluzhnyi.

Ukraine is apparently wary of the mercenary group's fighters possibly being relocated to Belarus following Prigozhin's aborted mutiny in Russia. A media report said new camps for Wagner troops are being built in Belarus.

Meanwhile, Ukraine's military intelligence agency announced on Friday that Russia is gradually reducing the number of personnel at the Russian-held Zaporizhzhia nuclear power plant.

It said three employees of the Russian state nuclear firm Rosatom were among the first to leave.

The agency went on to say that Ukrainian employees who signed a contract with Rosatom had also been advised to leave by July 5.

Remaining personnel have reportedly been told to blame Ukraine in the event of an emergency.

Zelenskyy said last week that Russia is planning an act of terrorism at the power plant. Russian Foreign Minister Sergey Lavrov said on Friday that Kyiv's claims are "pure lies."