The UN peacekeeping mission in Cote d'Ivoire (UNOCI) has released a statement saying forces loyal to Laurent Gbagbo, the country's incumbent leader, opened fire on civilians in Abidjan on Monday, killing about a dozen people.
The organisation said that in another incident, a group of pro-Gbagbo youths put a tyre around a young man and burnt him alive in the Riviera area of the city, and that another group "savagely attacked" two UN staff.
"With the increase in human rights violations and barbaric practices, there are grounds for wondering whether President Gbagbo is still in charge of his forces and supporters," Tuesday's statement said.
"UNOCI believes it is imperative to end this spiral of violence by finding a definitive solution to the political impasse which stemmed from the post-electoral crisis."
Gbagbo's camp was not immediately available to comment on the UN statement.
The UN statement came as forces loyal to Ouattara, the internationally-recognised winner of the country's presidential elections in November, seized the towns of Daloa, Bondoukou and Belleville.
On Monday, pro-Outtara forces took control of the town of Duekoue.
A source in the pro-Gbagbo military said Daloa and Duekoue had fallen, but fighting continued in parts of Duekoue.
"The combat was very violent in Daloa the whole night, but we couldn't keep our positions ... It has fallen into rebel hands," the source said.
The capture of Daloa and Duekoue, potentially open up a route to the major exporting port of San Pedro and the area the supporters of Outaeea now control produces about 600,000 tonnes of cocoa a year, half of Cote d'Ivoire's output.
San Pedro ships out about that amount each year.
Cocoa futures were lower on Tuesday, down 3.3 per cent in London in afternoon trading, as the market closely watched conflict which has pushed them to 30-year highs in past months.
The pro-Outtara forces, which Ouattara has recognised as his military and renamed the Cote d'Ivoire Republican Forces (FRCI), have controlled northern Ivory Coast since the civil war of 2002-3.
The disputed presidential election, which Gbagbo refuses to concede, has rekindled the civil war it was meant to finally end.
Heavy fighting has rocked Abidjan and across much of a north-south ceasefire line.
Up to one million Ivorians have now fled fighting in the main city of Abidjan alone, according to the UN refugee agency.
Others have been uprooted across the country and at least 112,000 have crossed into Liberia to the west.
Helicopter shot at
The UN peacekeeping mission also said on Tuesday that FRCI fighters in Duekoue had fired on one of its reconnaissance helicopters.
The aircraft have previously been targeted by Gbabgo's forces, but this was the first report of an attack by pro-Ouattara forces.
Ouattara remains holed up in a lagoon-side Abidjan hotel.
Tuesday's UN report of more civilians killed adds to a tally of 462 confirmed deaths since the crisis begin.
Human rights groups say crimes against humanity may have already been committed.
The world body is also investigating allegations that 200 African nationals, from Mali, Burkina Faso, Senegal, Guinea and Togo, were killed near Guiglo, southwest of Duekoue.