Twenty one people have been injured in a grenade blast in Rwanda's south-western town of Kamembe, police say.
It exploded in a business area of the town in the early hours of Tuesday evening.
No-one has been arrested in connection with the attack near the border with the Democratic Republic of Congo.
Police have blamed many previous attacks on rebels from the Hutu ethnic group involved in the 1994 genocide that killed about 800,000 people.
The BBC's Geoffrey Mutagoma in capital, Kigali, says there have been about seven blasts in Rwanda since last year.
Most of them have taken place in Kigali.
More than 30 people are on trial for the explosions, blamed on the FDLR rebel group based in DR Congo.
The government says it is waging an organised campaign to destabilise Rwanda and has vowed to pursue its commanders.
But it is too early to link the latest attack with previous ones, our reporter says.
Human rights campaigners say the Rwandan government, led by President Paul Kagame, has failed to pursue genuine reconciliation since the end of the genocide and has targeted the opposition.
A team of Commonwealth observers in Rwanda said there had been no real competition in last year's presidential election, after some candidates were barred from standing.
In January, four former top officials who had fallen out with Mr Kagame and gone into exile were sentenced in absentia to long jail terms for threatening state security and promoting ethnic divisions.