Russia ordered civilians to leave a swath 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.

People walk to board a ferry during the evacuation of Kherson residents

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 (9-mile) 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, but that Russia might be planning such actions itself to blame Ukraine.

The mouth of the wide Dnipro River has become one of the most consequential frontlines in the war in recent weeks, with Ukrainian forces advancing to expel Russian troops from their only pocket on the west bank. Russia has thousands of troops there and has been trying to reinforce the area. Ukraine's advance has slowed in recent days, with commanders citing weather and tougher terrain.

Saldo, the Russian-imposed occupation leader for the province, identified seven towns on the east bank that would now be evacuated, comprising the main populated settlements along that stretch of the river.

The European Union accused Moscow on Tuesday of launching a new programme to illegally conscript men in Crimea, which Russia seized in 2014, to fight in its forces. The EU statement said Moscow was disproportionately conscripting members of Crimea's indigenous Tatar minority to fight in its war.

Russia, which launched its "special military operation" in Ukraine in February, has announced it has completed a mobilisation drive ordered in September by President Vladimir Putin, saying it had called up 300,000 reservists and no more were needed.

But the Kremlin said on Tuesday Putin would not issue a new decree formally ending the mobilisation. That has raised concern it could be restarted without notice.

Thousands of Russian men have fled abroad to escape conscription to a conflict which has killed thousands, displaced millions, shaken the global economy and reopened Cold War-era divisions.