Russian forces are continuing their offensive to take full control of the eastern Ukrainian region of Luhansk, but they are facing resistance from Ukrainian troops.

The Russian military is stepping up its attacks on the key city of Severodonetsk.

Ukrainian military chiefs said on Sunday that the Russian side is using drones to conduct round-the-clock surveillance and is shelling populated areas.

The Russian Defence Ministry said on Saturday that its troops had attacked neighboring Lysychansk and destroyed fuel and oil refining facilities.

Luhansk Governor Serhiy Haidai said the Russian military now controls most parts of Severodonetsk, but the fighting in Donbas is not going as it planned.

The British Defence Ministry said on Sunday that in recent days, both Russia and Ukraine have continued to conduct heavy artillery bombardments on axes to the north, east and south of the Severodonetsk pocket, but with little change in the front line.

The ministry also noted low morale among Russian soldiers and cited "very heavy casualties, combat stress" and "limited opportunity for rotation of units out of combat" as some of the reasons.

Ukrainian President Volodymyr Zelenskyy posted a video on social media on Sunday after visiting frontline soldiers in the southern regions of Mykolaiv and Odesa the previous day.

He said, "Their mood is confident, they all do not doubt our victory. We will not give away the south to anyone, we will return everything that's ours."