The African Union and the United Nations have raised concerns about clashes in Burundi between rival supporters during campaigns ahead of next Wednesday’s election.

They have appealed to all sides to refrain from acts of violence and urged the security forces to ensure it's a fair election.

Human rights groups say close to 150 opposition members have been arrested since Burundi's election campaign began three weeks ago.

President Pierre Nkurunziza is not running for re-election but is expected to remain politically powerful after the government approved legislation that gives him the title of "paramount leader" after he steps down.