Ukrainian President Volodymyr Zelenskiy said on Saturday his government was ordering the mandatory evacuation of people in the eastern Donetsk region, scene of fierce fighting with Russia.

In a late-night television address, Zelenskiy also said the hundreds of thousands of people still in combat zones in the larger Donbas region, which contains Donetsk as well as the neighboring Luhansk region, needed to leave.

"The more people leave (the) Donetsk region now, the fewer people the Russian army will have time to kill," he said, adding that residents who left would be given compensation.

Separately, domestic Ukrainian media outlets quoted Deputy Prime Minister Iryna Vereshchuk as saying the evacuation needed to take place before winter begins since the region's natural gas supplies had been destroyed.

Zelenskiy said hundreds of thousands of people were still living in areas of Donbas where fighting was fierce.

"Many refuse to leave but it still needs to be done," the president said. "If you have the opportunity, please talk to those who still remain in the combat zones in Donbas. Please convince them that it is necessary to leave."

It is not the first time Ukrainian authorities have called for civilians to evacuate areas they control in Donetsk, and John Herbst, a former US ambassador to Ukraine, told Reuters it could be due to expectations of heavier fighting rather than fuel shortages.

"I don’t know why Zelenskiy issued the call," he said. "What I do know is that there has been fierce fighting in Donetsk. The Russians took (neighbouring) Luhansk (oblast) several weeks ago. I expect further fierce fighting in Donetsk."

Herbst said he did not expect Russia to capture the rest of Donetsk given the longer logistics lines they would need and the Ukrainian forces’ use of advanced long-range artillery and rocket systems provided by the United States and others.

Earlier on Saturday, Ukraine's military said more than 100 Russian soldiers had been killed and seven tanks destroyed in fighting in the south on Friday, including the Kherson region that is the focus of Kyiv's counteroffensive in that part of the country and a key link in Moscow's supply lines. (Reuters)