Russia ordered civilians to leave a swathe of Ukraine along the eastern bank of the Dnipro river, a major extension of an evacuation order that Kyiv says amounts to the forced depopulation of occupied territory.

Russia had previously ordered civilians out of a pocket it controls on the west bank of the river, where Ukrainian forces have been advancing to capture the city of Kherson. Russian-installed officials said on Tuesday they were now extending that order to a 15-km buffer zone along the east bank as well.

Ukraine says the evacuations include forced deportations from occupied territory, a war crime. Russia, which claims to have annexed the area, says it is taking civilians to safety because of a threat Ukraine might use unconventional weapons.

“Due to the possibility of the use of prohibited methods of war by the Ukrainian regime, as well as information that Kyiv is preparing a massive missile strike on the Kakhovka hydroelectric station, there is an immediate danger of the Kherson region being flooded,” Vladimir Saldo, Russian-installed head of occupied Kherson province, said in a video message.

“Given the situation, I have decided to expand the evacuation zone by 15 km from the Dnipro,” he said. “The decision will make it possible to create a layered defence in order to repel Ukrainian attacks and protect civilians.”

Moscow has accused Kyiv of planning to use a so-called “dirty bomb” to spread radiation, or to blow up a dam to flood towns and villages in Kherson province. Kyiv says accusations it would use such tactics on its own territory are absurd.