Ukrainian forces struggled to hold their ground in bloody street-to-street fighting in the eastern front-line city of Sievierodonetsk as President Volodymyr Zelenskyy said the situation was difficult, also pledging to retake Russia's gains.

The dayslong battle for the industrial city has emerged as pivotal, with Russia focusing its offensive might in the hope of achieving one of its stated aims — to fully capture surrounding Luhansk province on behalf of Russian-speaking separatists.

"We have to achieve a full deoccupation of our entire territory," Zelenskyy said during a virtual appearance at an event hosted by Britain's Financial Times newspaper on Tuesday.