Ukraine is widely expected to launch a counteroffensive in the coming weeks to recapture territory from Russian forces, aided by an influx of sophisticated weapons from its Western allies. Although the Ukrainian authorities have said that the precise location of that push remains a closely guarded secret, military analysts and some Ukrainian officials have said that it could focus on the south of the country.

On Saturday, the Ukrainian military's General Staff said that the Russian authorities were encouraging Ukrainian citizens in occupied parts of the Zaporizhzhia and Kherson regions of southern Ukraine to get Russian passports and then move south to the Crimean Peninsula. Russia illegally annexed Crimea in 2014, and then did so with Zaporizhzhia and Kherson last October in a move that was widely condemned.

"The Russian occupiers intensified preparations for the evacuation of the local population in the temporarily occupied territories of Zaporizhzhia and Kherson," the General Staff said in its morning update. In the cities of Melitopol and Skadovsk in the Zaporizhzhia region, it said, the occupation authorities conducted a survey about possible evacuation and checked that residents had Russian identity documents.

"The invaders are spreading information that the forced evacuation of the civilian population will begin at the end of April," the General Staff update said.

While Moscow has occupied all of Crimea, it only has partial control of Zaporizhzhia and Kherson. In recent weeks, both Russia and Ukraine have been massing their forces along the front line in the Zaporizhzhia region amid the speculation of a possible Ukrainian counteroffensive there.