A US think tank says the Ukraine military seems to be advancing and retreating on the battlefield against Russia. President Volodymyr Zelenskyy called on the Ukrainian people to be unified.

Ukrainian media quoted an official of the country's military as saying that Russia had concentrated about 10,000 personnel in the contested city of Bakhmut in the eastern region of Donetsk, and that fierce battles continue there.

Russia continued attacks on Ukraine using drones and other weapons on Sunday.

The governor of the eastern region of Dnipropetrovsk said Russian drone attacks had caused damage to civilian infrastructure facilities and power lines.

Last year, Russia targeted energy infrastructure in Ukraine, causing major power outages when temperatures were falling in the run-up to winter.

A US think tank, the Institute for the Study of War, said in its assessment on Saturday that Russian forces apparently "recaptured limited positions at a series of previously lost Russian defensive positions south of Robotyne."

The Ukrainian military announced in August that Robotyne in the Zaporizhzhia region had been liberated.

People in Ukraine have paid respect for members of the country's armed forces who have lost their lives and those who are fighting to defend their homeland.

At a Day of Defender event in the capital Kyiv on Sunday, President Volodymyr Zelenskyy reiterated his call for national unity, saying that Ukrainian courage would bring peace to the country.