Ukraine's President Volodymyr Zelenskyy on Sunday acknowledged that Kyiv's forces had withdrawn from Lysychansk in the eastern Donbas region, but vowed to regain control over the area with the help of long-range Western weapons.

Earlier, Ukraine's military command confirmed that its forces had been forced to retreat from the city after Russia claimed control.

"The continuation of the defense of the city would lead to fatal consequences. In order to preserve the lives of Ukrainian defenders, a decision was made to withdraw," it said in a statement on social media.

In a nightly video address, Zelenskyy also said that the Ukrainian forces are now gradually pressing in Kharkiv, Kherson and the sea.

(With input from Reuters)