Assailants attacked numerous polling stations in Burundi overnight, disrupting the start of voting in controversial polls that follow two months of unrest over the president's bid for a third term.
Armed groups threw grenades at stations in both the capital Bujumbura and in some provinces ahead of Monday's parliamentary and local elections, delaying the start of voting in many of the centres, police and election officials said.
"Voting has not yet begun in many centres in the capital because election officials are trying to prepare materials and in almost all of the stations, these arrived late because of the overnight attacks," Cyriaque Bucumi, the president of the Bujumbura electoral commission, told AFP.
The opposition and civil society groups are boycotting Monday's polls, saying the elections - which the authorities have refused to delay despite calls from the international community - will not be free and fair.
Burundi has been roiled by weeks of unrest that has included widespread protests and a failed coup bid and that has killed more than 70 people and send thousands fleeing the central African country following President Pierre Nkurunziza's bid for a third term.
Monday's vote is for local and parliamentary seats, with a presidential election due to follow on July 15.
Burundi was plunged into turmoil in late April when Nkurunziza launched his drive for a third consecutive five-year term, triggering widespread protests.
Opponents say his bid for another term is unconstitutional and violates a peace accord that paved the way to end 13 years of civil war in 2006.
Several top officials - including the deputy vice-president Gervais Rufyikiri as well as members of the election commission and constitutional court - have also fled the poverty-stricken, landlocked country.