Ukrainian soldiers take up positions in the Donetsk region, Ukraine. File/AP

Ukrainian troops are holding out against repeated attacks by Russian forces in two eastern towns while those on the southern front are poised to battle for the strategic Kherson region, which Russia appears to be reinforcing.

Ukrainian President Volodymyr Zelensky said in a Wednesday evening video address that there would be good news from the front but he gave no details.

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He did not mention what was happening in Kherson in the south, which officials and military analysts have predicted will be one of the most consequential battles of the war since Russia invaded Ukraine eight months ago.

The most severe fighting in eastern Ukraine was taking place near Avdiivka, outside Donetsk, and Bakhmut, Zelensky said.

Evacuees from Kherson gather upon their arrival at the railway station in Anapa, southern Russia, on Tuesday. AP

"This is where the craziness of the Russian command is most evident. Day after day, for months, they are driving people to their deaths there, concentrating the highest level of artillery strikes," he said.

Russian forces have repeatedly tried to seize Bakhmut, which sits on a main road leading to the Ukrainian-held cities of Sloviansk and Kramatorsk.

The looming battle for Kherson city at the mouth of the Dnipro River will determine whether Ukraine can loosen Russia's grip on the south.

The Russian-appointed Kherson regional government said it had rebased to the left bank of the Dnipro, Russia's RIA news agency reported, as forces braced for an increase in fighting.

Soldiers stand guard on a road before the expected evacuation. File/Reuters

While much of the front line remains off limits to journalists, at one section north of the Russian-occupied pocket on the west bank of the Dnipro, Ukrainian soldiers said Russian shelling was stepping up again after having tailed off in recent weeks.

Radio intercepts indicated freshly mobilised recruits had been sent to the front and Russian forces were firmly dug in.

"They have good defensive lines with deep trenches, and they are sitting deep underground," said Vitalii, a Ukrainian soldier squatting in a weed-choked irrigation canal, concealed from any prowling enemy drones by overhanging trees.

Ukrainian forces advanced along the Dnipro in a dramatic push in the south at the start of this month, but progress appears to have slowed. Russia has been evacuating civilians on the west bank but says it has no plans to pull out its troops.

Oleksii Reznikov, Ukraine's defence minister, said wet weather and rough terrain were making Kyiv's counter-offensive in Kherson harder than it was in the northeast, where it pushed Russia back in September.

At the front, intermittent artillery fire echoed from both sides, with towers of smoke rising in the distance.

Reuters