Ukraine told its forces to withdraw from Sievierodonetsk, an eastern city that has been the center of fighting for weeks.
The military concluded that Ukrainian troops were at risk of being surrounded by Russian invaders who repeatedly attacked their positions.
“Staying in positions that have been relentlessly bombed for months just doesn’t make sense,” Luhansk governor Serhiy Haidai told Ukrainian television on Friday.
The soldiers will retreat to new positions while the Russians attack the nearby city of Lysychansk.
Russian President Vladimir Putin is focusing his unprovoked attack on Ukraine in the eastern region of Donbass, after failing to take Kyiv at the start of the war that began on February 24.
The Russians have slowly taken control of territory in the eastern and southern parts of Ukraine, including the devastated city of Mariupol, while building a corridor from Russian territory to Crimea, which it annexed in 2014.
While suffering on the battlefield, Ukraine won a victory when the European Union granted its request this week to be a candidate for membership. Ukrainian President Volodymyr Zelenskyy called the moment “unique and historic”.
Mr. Zelenskyy also thanked President Biden on Friday for committing $450 million in additional defense aid.
“By joint efforts, we will liberate Ukrainian land from the Russian aggressor!” he tweeted.