The death was revealed of artillery commander Lt Col Vladimir Nigmatullin, a father of three, from Yekaterinburg, the fourth-largest city in Russia.
He was killed on 31 May but his loss to Russian forces was only disclosed on Tuesday.
Russia has lost on average almost one colonel every two days in the bloody conflict in Ukraine which was triggered by Vladimir Putin.
Nigmatullin’s death was confirmed by his family. He is believed to have been aged 46.
The exact circumstances of how he died have not been revealed.
His sister-in-law Marina Konyukhova posted on social media:“Eternal memory, darling, dear, much-loved man, you passed away.
“We still cannot believe you are gone. You are a father of three children, and an amazing husband to my sister. “I am always proud of you, and I will always be proud.
“You set an example to the Motherland, so that everyone does like you did. You were ordered with the Order of Bravery, posthumously.
“You went through a lot of conflict areas.”
His death comes as Russia lost its 11th general of the conflict in recent days, Major-General Roman Kutuzov was the chief of staff of the 29th Combined Arms Army.
It was revealed onTuesday that he was awarded a posthumous promotion to Lieutenant-General.
He died in an ambush in Donbas.
“He calmly walked up the career ladder, successfully commanded the troops, and died as a soldier, fighting on the front lines,” said a report by Readovka.
A picture showed Kutuzov’s funeral in Russia.
One mourner said: “I knew him personally, Roman lived a hero and died a hero.
“My condolences to his loved ones, strength and patience to his subordinates and fellow officers.”
Some sources have claimed that Russia lost a second and more senior general in the same incident in Donetsk region.
If his death is confirmed he will be the 12th general to have been killed in the war.
