The 21-year-old sergeant, Vadim Shishimarin, pleaded guilty to the killing of a 62-year-old civilian in northeast Ukraine in the first days of the Kremlin's offensive.
The first Russian soldier on trial in Ukraine for "war crimes" during Moscow's attacks has pleaded guilty, facing possible life imprisonment in Kiev.
Asked in court if he was guilty of the allegations, including war crimes and premeditated murder, 21-year-old sergeant Vadim Shishimarin responded "yes" on Wednesday.
He is accused of killing a 62-year-old civilian in northeast Ukraine in the first days of the Kremlin's offensive.
Shishimarin — from the Siberian region of Irkutsk — sat in the glass defendant's box in a Kiev district court, wearing a blue and grey hoodie.
The soldier looked towards the ground as a prosecutor read out charges against him in Ukrainian. An interpreter was translating for him into Russian.
Civilian killed on bicycle
He is accused of killing the civilian — allegedly on a bicycle — near the village of Chupakhivka in the eastern Sumy region on February 28.
Prosecutors say Shishimarin was commanding a unit in a tank division when his convoy came under attack.
He and four other soldiers stole a car, and as they travelled near Chupakhivka they encountered a 62-year-old man on a bicycle, they said.
According to prosecutors, Shishimarin was ordered to kill the civilian and used a Kalashnikov assault rifle to do so.
The Kremlin earlier said it was not informed about the case.