A Ukrainian military spokesperson says the intensity of Russian attacks in the battleground city of Bakhmut has significantly declined. But a senior Ukrainian official has warned that Russia is regrouping its forces for expected fighting.

A Ukrainian media outlet on Sunday quoted the spokesperson as saying Russian troops continue shelling the positions of Ukrainian forces near Bakhmut in the eastern region of Donetsk. But the spokesperson adds that only one military clash has occurred there since Saturday.

The leader of the Russian private military firm Wagner Group, Yevgeny Prigozhin, said on Thursday that his units are transferring their positions in Bakhmut to regular Russian troops.

Ukraine's National Security and Defense Council Secretary Oleksiy Danilov confirmed the withdrawal of some Wagner forces from the city in an interview with the British public broadcaster, the BBC.

But Danilov said it does not mean Wagner personnel will stop fighting Ukrainian forces. He added that they will regroup to concentrate more on other fronts.

The regrouping is believed to be part of Russian efforts to prepare for Ukraine's widely anticipated major counteroffensive.

Meanwhile, Russia unleashed a massive drone strike on the Ukrainian capital, Kyiv, early on Sunday. The Ukrainian Air Force says it shot down 52 of 54 drones used in the attack.

Russia has recently launched repeated intensive rounds of drone and missile strikes on the city and other Ukrainian areas.

Ukrainian President Volodymyr Zelenskyy said on Sunday that his country's air defense forces are heroes as they save lives by intercepting enemy drones and missiles.