Russia has lost another colonel as Ukraine continues to inflict punishing losses on Vladimir Putin's top brass.

Mikhail Nagamov, 41, the commander of a sapper regiment, died fighting in Ukraine

It is not clear how or where exactly Nagamov died, with reports saying only that he perished 'performing a combat mission in Ukraine'. He leaves behind a wife and child in the village of Suslonger, around 400 miles east of Moscow.

Nagamov's death is just the latest suffered among Russia's command corps, with dozens of colonels and eight generals having been killed by Ukraine.

The country's military claims to have killed almost 21,000 Russian soldiers since Putin gave the order to invade on February 24, along with hundreds of tanks and thousands of other vehicles.

Russia has also lost the warship Moskva, the flagship of its Black Sea Fleet, despite Ukraine not possessing a navy.

And the bloodletting is sure to ramp up again as Putin presses his generals back into battle in Ukraine's east in an attempt to capture the Donbas region.

President Volodymyr Zelensky said on Tuesday that Russia had begun its assault on the region, amid a massive barrage of artillery along a 300-mile stretch of frontline near Donetsk and Luhansk and an uptick in fighting.

Ukraine reported battles around the city of Izyum, where Russia has massed most of its assault forces, as well as around Severodonetsk and Lysychans'k.

Kremmina, a small town to the north of Severodonetsk, was captured by Russian troops Tuesday when Ukrainian forces retreated because there was 'nothing but rubble to defend' after weeks of bombardment.

But Ukraine had counter-attacked elsewhere: Claiming to have re-taken the town of Marinka, near Donetsk, and seized towns to the east of Kharkiv - putting Russian supply lines under threat.

, according to articles that have appeared in Russian media.