Protesters have taken to the streets of Haiti's capital to demand the suspension of a runoff presidential vote over alleged irregularities.

The demonstrations in Port-au-Prince on Monday came as attackers in rural areas set fire to several electoral offices.

Some of the thousand-strong group of protesters burned vehicles, threw rocks and attacked a petrol station in the downtown area of the capital.

Haiti is due to hold a runoff vote backed by international donors on Sunday, but tensions have risen since the opposition candidate Jude Celestin said last week he would withdraw.

Celestin accuses electoral authorities of favouring the ruling party.

"We are moving towards a selection, not an election," Celestin told the Associated Press on Saturday.

The Swiss-trained engineer came second in an October first-round vote in the poor Caribbean nation, beaten by banana exporter Jovenel Moise, the ruling party candidate.

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.

Fresh elections

Monday's protesters demanded the creation of an interim government and that fresh elections be held after President Michel Martelly leaves office in February.

They included several opposition groups including the Platform Pitit Desalin and supporters of the opposition candidate, Celestin.

"We declare this week the rebellion week to block the January 24 election. We will protest in front of each voting booth and voting centre," said Assad Volcy, secretary-general of Pitit Desalin.

In the north of the country, unknown assailants burned four offices belonging to the electoral council, which has been blamed by many critics 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.