Demonstrators run past burning tires during a protest in Port-au-Prince on Thursday. (Emilio Morenatti/Associated Press)Haitians angry over the cholera epidemic ignored exhortations from health workers to stop violence that is disrupting treatment efforts, and authorities feared more unrest in the capital Friday.

Violence spread into Port-au-Prince for the first time Thursday after three days of upheaval in the country's north. Protesters threw rocks at UN peacekeepers, attacked foreigners' cars, blocked roads with burning tires and toppled light poles.

The upheaval over a cholera outbreak that has killed more than 1,100 people comes before national elections Nov. 28.

UN officials argue that the violence is being encouraged by forces that want to disrupt the ballot, and some demonstrators Thursday threw rocks at an office of President René Préval's Unity party and tore down campaign posters.

A protester holds up a sign during a demonstration against the UN mission in downtown Port-au-Prince on Thursday. (Allison Shelley/Reuters)

But the anger is fuelled by suspicions that a contingent of Nepalese soldiers brought cholera with them to Haiti and spread the disease from their rural base into the Artibonite River system, where the initial outbreak was centred last month. It is a suspicion shared by some prominent global health experts.

Cholera had not been recorded before in Haiti despite rampant bad sanitation and poor access to drinking water, problems that cause outbreaks of the disease in other parts of the world. Cholera is endemic to Nepal, where there was an upsurge before the Nepalese troops came to Haiti.

Experts have not pinpointed the origin of Haiti's epidemic, however, and the 12,000-member UN stabilization mission in Haiti, or MINUSTAH, denies responsibility.