United Nations troops have shot dead three people as crowds attacked the UN compound in the Democratic Republic of the Congo capital, Kinshasa.
The UN has been blamed for the fall of Bukavu
Protestors in several Congolese cities have blamed the UN for failing to prevent the eastern town of Bukavu from falling to dissident soldiers.
Recent fighting in the east has sparked fears that DR Congo's fragile peace
process may be unravelling.
Meanwhile, the rebel leader has said his fighters will leave Bukavu.
The protests against the UN began on Wednesday, when news broke that the town had fallen.
Anti-UN protests have also been reported in Bukavu, Kisangani and Kindu.
"Three Congolese were killed during the demonstration as they were basically trying to loot our facility in Kinshasa," UN peacekeeping chief Jean-Marie Guehenno said at UN headquarters in New York on Thursday.
"Our troops had, as a last resort, to open fire."
Latest reports from Bukavu say the rebels have begun to withdraw from Bukavu - a day after they seized the town.
Local rebel leader Gen Laurent Nkunda said he had already ordered 300 fighters to leave Bukavu and the rest would depart later but remain "around" the town.
Renegade commanders - who are ethnic Banyamulenge, related to Rwandan Tutsis - say government forces have been attacking members of their community.
Gen Nkunda told the BBC's Rob Walker in Bukavu that he did not want to control the town, merely to protect the Banyamulenge.
The dissident soldiers are from a former Rwandan-backed rebel group that was supposed to join the national army.
Additional UN peacekeepers were sent to Bukavu last week, following fighting between the dissidents and regular troops.
But the 1,000-strong UN force did not oppose the advancing rebel fighters, saying it did not have a mandate to "make war".
Gen Nkunda has several thousand men under his control. They are reinforcing Col Jules Mutebusi, whose militia first clashed with the army last week.
DR Congo President Joseph Kabila has accused neighbouring Rwanda of being behind the rebels.
Bukavu is "under the control of Rwandan occupants", he said, telling the BBC it was "a situation of war".
Rwanda has denied any involvement.
Kinshasa says Gen Nkunda is receiving orders from Rwanda
The UN said Rwandan troops had been spotted in DR Congo north of Bukavu six weeks ago, although they were all supposed to have left as part of last year's peace deal.
While Rwanda has denied having any troops in DR Congo, Foreign Minister Charles Muligande said that Rwanda would intervene to oppose "genocide".
A week of clashes has left dozens of people dead, and thousands have fled into Rwanda.
Both Col Mutebusi and Gen Nkunda are former members of the largest rebel group, the RCD, which controlled all of eastern DR Congo during the five-year war.
Under a peace deal agreed last year, all the Congolese warring factions were supposed to unite as a single army, but progress has been slow.
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