A colleague presented six new grenades as a gift to Chastiakov, who was a top aide and close friend to Zaluzhnyi, Klymenko said.
He said Chastiakov was showing off the grenades to his family at home when his son took one and began twisting the ring.
“The serviceman then took the grenade from the child and pulled the ring, leading to a tragic explosion,” Klymenko said.
The officer's death was the second fatal tragedy in less than a week for Ukraine's military.