The UN has opened an investigation into reports that its troops killed two Congolese civilians during protests in the eastern city of Goma, amid fighting with rebels.
Eyewitnesses told the AFP news agency the two died on Saturday when a crowd tried to storm a UN base and said troops from Uruguay had opened fire.
Uruguay has denied the allegations and blamed the Congolese police.
A new UN intervention brigade is deploying to the area to tackle rebels.
UN troops last week shelled rebel positions just outside Goma.
There has been no official statement on how many people have died in the fighting.
One local doctor has told the AP news agency he had seen 82 dead bodies, including those of 23 government soldiers on Sunday.
"I'm overwhelmed by what I've seen: bodies blown apart, arms and feet here and there," said Isaac Warwanamiza, speaking from a hospital north of Goma.
Many Congolese accuse the 18,000-strong UN mission in the Democratic Republic of Congo of not doing enough to end two decades of conflict in the east of the country.
Hundreds of people reportedly joined Saturday's protests, after rockets killed several civilians in the city, and called for the UN to attack the M23 rebel group.
Augustin Matendo, one of the protesters, told AFP that Uruguayan troops opened fire.
"Two people were killed instantly and four others were injured and rushed to hospital," he told AFP.
Uruguay President Jose Mujica denied the claims.
The UN intervention brigade has the strongest mandate ever given to such a peacekeeping force and is tasked with eradicating the rebel groups which have plagued eastern DR Congo since 1994.
On Sunday, the UK pulled its Foreign Office staff out of the city due to security concerns, while the US condemned the rebel attacks.
In November, the M23 rebels briefly captured Goma, which borders Rwanda, withdrawing in exchange for a series of demands, including negotiations with the government.
Rwanda has repeatedly denied UN allegations that it has been backing the M23 rebels.
Like Rwanda's leadership, M23 fighters mostly come from the Tutsi community.
They deserted from the Congolese army in April 2012, forcing an estimated 800,000 people from their homes in the ensuing unrest in the mineral-rich region.
Peace talks taking place in Uganda this year to resolve their grievances have stalled.