Stone-throwing protesters have taken to the streets of Haiti’s capital Port-au-Prince to demand the suspension of a runoff presidential election over alleged irregularities.
In rural areas unknown attackers burned several electoral offices.
Haiti is due to hold a runoff vote on January 24, but tensions have risen since the opposition candidate Jude Celestin said last week he would withdraw on the grounds that electoral authorities favoured the ruling party.
Swiss-trained engineer Celestin, 53, came second in an October first-round vote in the poor Caribbean nation, beaten by banana exporter Jovenel Moise, 47, the ruling party candidate.
Accompanied by a man playing trumpet, the several thousand-strong crowd grew angrier as it moved from poor neighbourhoods into downtown Port-au-Prince. Some protesters burned vehicles, threw rocks and attacked a petrol pump.
Elections and transfers of power in Haiti have long been plagued by instability, and international observers said October's vote was relatively smooth. However, several of the 54 candidates said the government had twisted the results.
Monday's protesters demanded the creation of an interim government and fresh elections after President Michel Martelly leaves office in February. They included several opposition groups, among them the Platform Pitit Desalin, and supporters of Celestin.
In the north of the country unknown assailants burned four offices belonging to the electoral council, blamed by many for irregularities in the October vote. Four members of the electoral council have resigned in recent days.
The election authority said it condemned acts of violence and vowed to go ahead with the vote on Sunday.