Russian troops have temporarily eased attacks in and around the besieged eastern Ukrainian city of Bakhmut to regroup and strengthen their capabilities, a senior Kyiv official said on Saturday.

Separately, senior Ukrainian officials indicated their forces were ready to launch a long-promised counteroffensive to recapture territory taken by Russia since the start of the conflict.

Russia's Wagner mercenary group began handing over positions to regular troops this week after declaring full control of Bakhmut following the longest and bloodiest battle of the conflict.

Kyiv, though, has insisted that its forces still control a small part of the city.

In a statement on Telegram, Ukraine's Deputy Defense Minister Hanna Maliar said Russian troops were continuing to attack but that overall offensive activity had decreased.

"Yesterday and today there have not been any active battles - neither in the city nor on the flanks," she wrote, adding that Moscow's troops were instead shelling the outskirts and approaches to Bakhmut.

"(Russian) troops are being replaced and regrouped," Maliar said. "The enemy is trying to strengthen its own capabilities."

Oleksiy Danilov, secretary of Ukraine's National Security and Defense Council, told the British Broadcasting Corporation that the push could begin "tomorrow, the day after tomorrow or in a week".

Presidential aide Mykhailo Podolyak, speaking to Britain's Guardian newspaper, said preliminary operations such as destroying supply lines or blowing up depots had already begun.

The governor of the southern Russian region of Belgorod said he had come under artillery fire on Saturday when trying to enter the town of Shebekino, which is only about 7 km (4.5 miles) north of the border with Ukraine.

"I couldn't even get out of the car. Shells were exploding in a neighboring street," Vyacheslav Gladkov wrote on Telegram. Ukraine-based ethnic Russian fighters were reported to be behind a cross-border raid into the region in the last week.

Ukraine's top general, Valeriy Zaluzhnyi, posted a sleekly produced video on Saturday showing Ukrainian troops swearing an oath and preparing for battle.

"The time has come to return what is ours," he wrote.