Serhiy Haidai made the statement in a television interview, the Reuters news agency reported.
Russia now controls most of the eastern Ukrainian city of Severodonetsk, which has seen intense "street-by-street fighting" over the past month, according to officials.
If Severodonetsk were to fall, nearby Lysychansk would become the last Ukrainian stronghold in Luhansk province.
Luhansk is one of two provinces that make up the eastern Donbas region, which Russia seeks to capture as one of its key war aims.
Haidai said of Severodonetsk: "Remaining in positions smashed to pieces over many months just for the sake of staying there does not make sense."
He added that Ukrainian units "have already received the order to move to new positions."
He also stated that 90 percent of the buildings in the city have been either destroyed or damaged, Polish state news agency PAP reported.
The Kremlin’s ‘fixation on Severodonetsk’
However, “the loss of Severodonetsk and Lysychansk will not represent a major turning point in the war,” according to the US-based think tank, the Institute for the Study of War.
The ISW said that “Ukrainian troops have succeeded for weeks in drawing substantial quantities of Russian personnel, weapons, and equipment into the area and have likely degraded Russian forces' overall capabilities while preventing Russian forces from focusing on more advantageous axes of advance.”
In other words, “Ukrainian forces have fundamentally accomplished their objective in the battle by slowing down and degrading Russian forces,” the think tank wrote.
Moreover, “the Kremlin’s ideological fixation on the capture of Severodonetsk, much like the earlier siege of Azovstal, will likely be to the ultimate detriment of Russian capabilities in future advances in Ukraine,” according to the ISW.
The think tank added: “The loss of Severodonetsk is a loss for Ukraine in the sense that any terrain captured by Russian forces is a loss—but the battle of Severodonetsk will not be a decisive Russian victory.”
Russia lacks aircraft personnel: UK
Meanwhile, the UK Ministry of Defence reported on Friday that Russia was struggling to support its invasion with sufficient aircraft personnel.
The report came after Ukrainian forces announced that the pilot of a Russian Su-25 Frogfoot ground-attack aircraft they shot down on June 17 turned out to be a former Russian air force major now working for the pro-Russian Wagner private military company.
The UK analysts wrote: “The use of retired personnel, now working as Wagner contractors, to conduct close air support missions indicates that the Russian air force likely is struggling to support its invasion of Ukraine with sufficient aircrew.”
Moreover, evidence suggests that “Wagner aircraft are older models of the Su-25 and that the Russian air force is not providing Wagner with up-to-date avionics equipment,” the British Ministry of Defence said.
Battle for Donbas continues
Ukraine’s General Staff reported on Friday that fierce fighting continued in the Donbas, notably "in the Severodonetsk direction."
Meanwhile, "in the Slovyansk direction," the "enemy fires artillery at civilian infrastructure in the areas of the settlements of Bohorodychne, Krasnopillya, Kurulka, Chervone, Ridne and Chervona Polyana,” it said.
Ukraine’s army command also reported that "in the Bakhmut direction," the "enemy fired at artillery positions of our troops near Mykolayivka, Berestove, and Novoluhansk.”
“It is trying to improve the tactical position and take control of the existing routes,” Ukrainian military officials said.
Elsewhere, in the direction of the northeastern city of Kharkiv, “the enemy inflicted artillery strikes in the districts of Kharkiv, Staryi Saltiv, Korobochkyne, Pechenihy, Dementiyivka, and Zolochiv,” according to Ukraine’s General Staff.
It added that Russian forces “intensified the activities of sabotage and reconnaissance groups.”
Friday is day 121 of the Russian invasion of Ukraine.
Source: PAP, Reuters, understandingwar.org, facebook.com/GeneralStaff.ua