At least four people were killed and 20 wounded when demonstrations against rising food prices turned into riots in southern Haiti, officials say.
Reports say scores of people went on the rampage in the town of Les Cayes, blocking roads, looting shops and shooting at UN peacekeepers.
The UN said its personnel had opened fire at some of the armed protesters.
For two days running, parts of Haiti have been erupting into violence triggered by the soaring cost of food.
The prices of rice, beans and fruit have gone up by 50% in the last year.
Earlier this week, UN Secretary General Ban Ki-moon issued a report saying that the food crisis threatened the Caribbean nation's fragile security.
Government food aid
The demonstrations against the high cost of living began on Thursday in a number of towns, but in some areas they turned into riots.
On Friday, thousands took to the streets again, with some blocking roads, burning cars and looting shops. A small group of protesters also broke into the UN compound in Les Cayes and damaged its gate.
Some also fired shots at peacekeepers deployed in the town in an attempt to maintain public order. The UN troops fired back in response.
The ensuing unrest left three dead in Les Cayes, including one young man who demonstrators said was fatally shot in the head by the UN peacekeepers. The UN said it was investigating the death.
Haiti's Prime Minister, Jacques Edouard Alexis, condemned the violence, but said the mass demonstrations had been manipulated.
"We know that these demonstrations have been infiltrated by individuals linked to drug dealers and other smugglers," he said.
Mr Alexis said he had made $10m (£5m) available for schemes to help fight the rising cost of food, including food aid and half-price fertiliser. He also announced job creation and credit programmes.
Haiti is one of the poorest countries in the Americas. Around 80% of the population lives on less than $2 (£1) a day.