A grenade attack in Burundi's capital Bujumbura has left four people dead, including a child.

A government official and witnesses said on Sunday the four were killed late Saturday in a bar in the working class Kinama neighborhood.

A hospital source said ten others were wounded in the attack.

In an earlier attack on Saturday "armed criminals" threw a grenade at a police patrol, injuring eight civilians, Bujumbura mayor Freddy Mbonimpa said.

Another grenade was also thrown at a military patrol, but no one was hurt.

No group claimed responsibility for the attacks.

The security situation in Burundi has been unstable since April 2015, when President Pierre Nkurunziza announced his bid to compete for a third presidential term.

The opposition stood against the move, arguing that the president's decision was in violation of the Constitution, which allows the president to run for two successive terms.

However, Nkurunziza's allies said his first term did not count as he was elected by the parliament and not by direct vote to end the civil war in the country.

Since then, about 200 people have been killed in violence with the situation worsening after Nkurunziza won a third term in the July presidential election.

Last month, United Nations High Commissioner for Human Rights Zeid Ra’ad Zeid Al Hussein expressed concern that the country risks sliding back into civil war.

Between 1993 and 2005 around 300,000 people died in Burundi as a result of civil war fought along ethnic lines.

The small central African state is estimated to have a population of 10.5 million people.

About 85 percent of Burundi's population are of Hutu ethnic origin and the rest are Tutsi.