Port-au-Prince, Haiti: 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 and blocked roads with burning tires and toppled light poles.

The upheaval over a cholera outbreak that has killed more than 1,100 people comes just days before national elections planned for 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 Rene Preval's Unity party and tore down campaign posters.

But the anger is fueled 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 centered 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 and there was an upsurge there 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.

UN peacekeepers have been the dominant security force in Haiti for six years, and there was resentment against them even before the cholera outbreak.

Standing before the thick black smoke of blazing tires Thursday, protesters in Port-au-Prince yelled "We say no to MINUSTAH and no to cholera." Some carried signs reading "MINUSTAH and cholera are twins." The windows of several cars belonging to the United Nations and to humanitarian groups were broken.

"It's not only that (the UN peacekeepers) have to leave but the cholera victims must get paid (damages)," said Josue Meriliez, one of the demonstrators.

Haitian police fired tear gas at the protesters on the central Champ de Mars plaza, and clouds of choking irritants blew into nearby tent shelters of thousands made homeless by the January 12 earthquake.

Protesters also threw rocks at a motorcade leaving the national palace, which fired warning shots to clear a path. It was not immediately known if President Rene Preval was in the motorcade.

Aid workers, including UN humanitarian agencies that are structurally separate from the peacekeeping force, have been calling for calm, saying the violence is hampering efforts to treat the tens of thousands of people stricken with cholera.

The disease is spread by contaminated fecal matter. Health experts say it can be easily treated with rehydration or prevented outright by ensuring good sanitation and getting people to drink only purified water.
But after years of instability, and despite decades of development projects, many Haitians have little access to clean water, toilets or health care.

In the neighbouring Dominican Republic, health authorities launched a nationwide search Thursday for people suffering from symptoms typical of cholera: diarrhea, vomiting and dehydration.

Health Minister Bautista Rojas said hundreds of doctors, epidemiologists and other medical officials will be going "house by house, in each sector, neighborhood and alleyway," looking for any trace of an outbreak.
They will interview neighbors, offer medical care and, if necessary, take anyone suspected of having cholera to the hospital.

The Dominican Republic has stepped up health measures to try to keep the epidemic from crossing the border - especially after the nation's first cholera case was detected Monday in an immigrant brick worker who returned sick after a vacation in his Haitian homeland.

Dominican authorities have increased border patrols and monitoring of frontier crossings. The two nations share the Caribbean island of Hispaniola.