Nearly 800 cases of rape, torture and murder were committed over eight months in Central African Republic, mostly by armed groups, according to a report by the UN mission MINUSCA.
The sheer volume of abuses points to the difficulties that new leaders are likely to face in restoring order to one of Africa's most historically unstable countries.
Central African Republic is due to hold elections on December 27, ending a fragile two-year transition marked by inter-communal violence that pitted militants drawn from the Christian majority against mostly Muslim armed groups.
MINUSCA's first human rights report, released on Friday, said 775 violations and abuses affecting at least 785 victims were committed between September 15, 2014, and May 31 - a period that followed a 2013 coup and is widely seen as calm by local standards.
Violence has recently intensified again, with more than 130 people killed since late September, although fighting halted briefly during the Pope's visit last month.
"Serious challenges remain given the lack of progress towards the disarmament of armed groups and the absence of a functioning state authority in much of the territory," said the 25-page report, based on testimonies from victims and witnesses.
The population of internally displaced people were among the most affected by the violence, particularly elderly women and children, the report said.
Many of the country's nearly 450,000 displaced live in enclaves beyond the reach of state authorities and French and UN peacekeepers, some in fiefdoms controlled by warlords.
Musa Gassama, director of MINUSCA's human rights division, urged authorities to change what the report called a "firmly rooted" culture of impunity in the former French colony.
While the UN said that around 24 arrests have been made based partly on information from the report, a planned Special Criminal Court has yet to materialise because it lacks funding.
The UN also called on Central African authorities to urgently deploy civil servants, including magistrates, throughout the territory "in order to re-establish state authority and the rule of law".
