United Nations chief Ban Ki-moon has called on the Democratic Republic of Congo to investigate last week's violence in which 134 people died.
The violence came during protests by the Bundu dia Kongo sect
The government says 87 people died but a UN spokesman in DR Congo told the BBC they estimated the true figure was 134.
The violence broke out after demonstrators, alleging fraud in recent elections, rampaged through several towns in the province of Bas Congo.
The disturbances were quelled by government troops.
The deaths followed protests by the Bundu dia Kongo group, which correspondents say has an ethnic-based following and campaigns for the secession of parts of western DR Congo.
They held protests in DR Congo's main port, Matadi, and the towns of Mwanda and Boma.
Police say a gun fight began when they raided the home of the sect's leader Nemwanda Seni in Matadi.
In Mwanda, members of the sect took control of the police station and freed prisoners.
During street protests, Bundu dia Kongo members chanted: "The Congo can't be rebuilt on corruption."
They are unhappy that the opposition-dominated provincial assemblies in Kinshasa and Bas Congo elected members of the ruling party as state governors.
They say the MPs must have been paid to do so.
President Joseph Kabila became DR Congo's first freely elected leader in 40 years after winning October's run-off presidential poll.
The local elections complete a peace process begun in 2002 when a five-year war that had drawn in much of the region ended.
Defeated presidential candidate Jean-Pierre Bemba and his Union for the Nation party did well in western DR Congo, while Mr Kabila owed his majority to a landslide in the east.
The UN has its largest peacekeeping force - 17,000 troops - in DR Congo.
On Tuesday, Prime Minister Antoine Gizenga named a new government after months of delay.
The government is tasked with running a country ravaged by years of misrule and conflict.