At least three people were killed in Burundi overnight Saturday, witnesses said, as tension rises a day before key polls in the central African nation that the UN warns should be postponed.

One was shot while another was killed in a grenade blast, according to witnesses. A soldier was killed by accident by a comrade during a raid on a house, adding to the more than 70 killed in weeks of violence and a failed coup sparked by President Pierre Nkurunziza's bid to stay in power for a third term. Parliamentary and local elections are set to be held on Monday, and a presidential vote on July 15.