Unidentified gunmen set fire to ballot papers and other material in a district polling station northeast of Burundi on Saturday, days before a parliamentary election that opposition parties have said they will boycott.

The first round of elections will take place on 29 June.

Election officials said the attack, which comes amid fears of renewed violence in the tiny central African state, appeared to be an isolated incident.

Prosper Ntahorwamiye, spokesman for the electoral commission CENI, said the gunmen attacked the polling station in the Ntega district of Kirundo Province early on Saturday, burning voting materials and ballot boxes ahead of parliamentary elections on Monday.

Ntahorwamiye said preparations for the election elsewhere were going smoothly.

“We have not registered any other similar attack so far to my knowledge,” he said.

Opposition parties say their boycott of the election is to protest President Pierre Nkurunziza’s bid for a third term in a later presidential vote. They have also voiced concerns that voting would not be fair, aggravating Burundi’s worst political crisis since a civil war ended in 2005.

United Nations Secretary-General Ban Ki-moon said on Friday voting should be postponed due to the prevailing political and security environment.

The United States has also said it was putting electoral assistance on hold because Nkurunziza was pressing ahead with an election timetable in the absence of conditions necessary for a credible vote.