A US think tank suggests Russia plans to use so-called 'Storm-Z' military squads that include prisoners to capture the eastern Ukrainian city of Avdiivka despite expecting heavy casualties.

Avdiivka is a stronghold in the Donetsk region for Ukrainian forces. Russian troops reportedly have already suffered severe losses in battles around the city.

The Institute for the Study of War said on Monday, "Russian forces continue to use 'Storm-Z' assault units predominantly made up of prisoner recruits in highly attritional infantry-led frontal assaults."

The think tank quoted a Ukrainian forces spokesperson as saying Russia is preparing to conduct "meat assaults" near Avdiivka and are training Storm-Z units.

It reported, however, those units have been introduced into battle with poor training and often sustained heavy losses.

The British defense ministry said last week it is likely Russia originally envisioned Storm-Z units as "relatively elite organizations," but that since at least spring 2023, the units have effectively become "penal battalions, manned with convicts and regular troops on disciplinary charges."

The Ukrainian military claimed on Tuesday that Russia has lost more than 300,000 Russian military members since it launched the invasion in February last year.

The British defense ministry puts the number of Russian personnel who have been killed or permanently wounded in the invasion at 150,000 to 190,000.