Ukrainian troops have withdrawn from the beleaguered frontline city of Avdiivka to avoid being encircled, new military chief Oleksandr Syrsky said Saturday, handing Russia its biggest symbolic victory following Kyiv's failed summer counteroffensive.

Russia has been trying to capture Avdiivka for months. It is the most significant territorial gain for Russian forces since they seized the eastern city of Bakhmut last May and comes ahead of the second anniversary of the start of the invasion.

"I decided to withdraw our units from the city and switch to defense on more favorable lines," Syrsky said on Facebook.