(Updates with prosecutor seeking life sentence)
By Max Hunder and Tom Balmforth
KYIV, May 19 (Reuters) - A Ukrainian state prosecutor asked a court on Thursday to sentence a Russian soldier to life in prison for killing an unarmed civilian in the first war crimes trial arising from Russia's Feb. 24 invasion.
Vadim Shishimarin, a 21-year-old Russian tank commander, asked widow Kateryna Shelipova to forgive him for the murder of her husband, Oleksandr, in the northeast Ukrainian village of Chupakhivka on Feb. 28.
"I acknowledge my blame ... I ask you to forgive me," he told Shelipova at the hearing on Thursday attended by Reuters.
He pleaded guilty to the murder on Wednesday.
Oleksandr Shelipov's killing was one of what Ukraine and Western nations say is a far wider picture: Ukraine has accused Russia of atrocities and brutality against civilians during the invasion and said it has identified more than 10,000 possible war crimes. Russia has denied targeting civilians or involvement in war crimes.
At Thursday's court hearing, Shishimarin cut a forlorn spectacle in a glass booth for defendants - boyish, dressed in a tracksuit and with his shaven head lowered.
The Kremlin has said it has no information about the trial and that the absence of a diplomatic mission in Ukraine limits its ability to provide assistance.
The widow told the court that on the day her husband was killed, she had heard distant shots fired from their yard and that she had called out to her husband.
"I ran over to my husband, he was already dead. Shot in the head. I screamed, I screamed so much," she said. She looked distraught and her voice trembled with emotion.
Shelipova told the court she would not object if Shishimarin was released to Russia as part of a prisoner swap to get "our boys" out of the port city of Mariupol, a reference to hundreds of Ukrainian soldiers who have given themselves up to Russia.
The trial takes place as much of Ukraine is gripped by the fate of its soldiers who it hopes Russia will hand over as part of an exchange. In Russia, some senior lawmakers have called for the Azov Regiment fighters to be put on trial.
Shelipova said her husband had been unarmed and was dressed in civilian clothes. They had a 27-year-old son and two grandchildren together, she added.
Ukrainian state prosecutors have said Shishimarin fired several shots with an assault rifle at a civilian's head from a car after being ordered to do so.
Asked if he had been obliged to follow an order that amounted to a war crime, Shishimarin said "no".
"I fired a short burst, three or four bullets," he told the court.
"I am from Irkutsk Oblast (a region in Siberia), I have two brothers and two sisters ... I am the eldest," he said. (Reporting by Max Hunder; Writing by Tom Balmforth; Editing by Alexandra Hudson, Nick Macfie and Frances Kerry)