A Ukrainian military commander has expressed his determination to repel Russia's assaults on the strategic eastern city of Bakhmut.

Ukraine's defense ministry wrote on social media on Saturday that Colonel-General Oleksandr Syrskyi has pledged to defend the city.

The ministry quoted Syrskyi as saying, "It is necessary to gain time to accumulate reserves and start the spring counteroffensive, which is not far off."

Russian forces claimed that they had intensified their offensive and taken control of the eastern bank of a river that runs through Bakhmut. Ukrainian troops have built their defensive lines on the river's western side.

Ukraine authorities said on social media on Saturday that in the southern region of Kherson, three civilians were killed in a Russian attack.

A US think-tank noted that Russian forces have built a defense line on the Crimean Peninsula, which Russia unilaterally annexed nine years ago.

The Institute for the Study of War said on Friday that such fortifications "may suggest that Russian forces are unsure of their ability to hold occupied territories in southern Ukraine in the long term."