Ukrainian service members watch while a tank fires toward Russian troops in the industrial area of the city of Sievierodonetsk, as Russia's attack on Ukraine continues, Ukraine June 20, 2022.

KYIV, June 23 (Reuters) - Ukraine will be accepted as a candidate to join the European Union on Thursday, a move that will boost the country's morale as the battle with Russian troops for two cities in the east reached what one official called a "fierce climax".

"We must free our land and achieve victory, but more quickly, a lot more quickly," Zelenskiy said in a video address on Thursday.

The war of attrition in the Donbas - Ukraine's industrial heartland - is most critical in the twin cities of Sievierodonetsk and Lysychansk, which straddle the Siverskyi Donets River in Luhansk province.

Ukrainian forces were defending Sievierodonetsk and the nearby settlements of Zolote and Vovchoyrovka, Luhansk Governor Serhiy Gaidai said on Thursday, but Russian forces had captured Loskutivka and Rai-Oleksandrivka to the south.

Moscow says Ukrainian forces in the city are surrounded and trapped.

But Gaidai told Ukrainian Television on Wednesday that Russian forces did not have full control of Sievierodonetsk.

Gaidai said all Lysychansk was within reach of Russian fire.

Britain's defence ministry said some Ukrainian units had withdrawn, probably to avoid being encircled.