Police spokesperson Eric Kayiranga said the attack took place last week in the southern town of Karamba.
“One threw the grenade into the market where people were gathered and the motorcycle continued,” Kayiranga said. He and other security sources decline to comment on any motive.
“We’re still working on who committed this,” Kayiranga said.
Grenade attacks are relatively common in the Great Lakes, where many of the devices are left over from the region’s many conflicts and are sometimes used by criminals to settle scores.
While there has generally been little crime in recent years in the central African country where 800 000 died in the 1994 genocide, there are occasional bombings.
In April 2008, a grenade thrown by an unknown attacker killed a policeman at the genocide museum in the capital Kigali.
Rwandan security take a tough approach under President Paul Kagame, who says it is vital to stop revenge attacks in a nation where many know and live near the killers of their families.
Pic: Rwanda flag