Ukrainian President Volodymyr Zelenskyy has called on the pubic to continue their all-out resistance against Russia's invasion. He says this is a crucial and decisive time, and enduring the coming year will mean enduring the entire war.

In a video address on Friday, Zelenskyy said every day and every night of this year has seen savage new battles. He said the most intense fighting is taking place at locations including Avdiivka, near Maryinka and Bakhmut in the eastern region of Donetsk, as well as Kupiansk in the eastern Kharkiv region.

The president said he had a telephone call with Turkish President Recep Tayyip Erdogan. He called for Turkey's cooperation in preventing Russia from disrupting security in the Black Sea which is used by Ukraine as an export route for farm produce.

Meanwhile the US think tank, the Institute for the Study of War, said in its analysis on Friday that Russian forces may intensify efforts to capture Kupiansk in the coming weeks.

It said Russia has a grouping of forces in the area that appears to be less degraded than the forces responsible for offensive efforts elsewhere in eastern Ukraine.

The institute said the Russian military appears to have conditions conducive to intensifying its operations in the direction of Kupiansk.