Between 400 and 500 people died following Togo's disputed elections in April, the UN says - far more than earlier official figures.
The protests were violently suppressed, the UN says
A report by the United Nations Human Rights Commissioner Louise Arbour also said that torture and degrading treatment of prisoners were widespread.
The government has disputed the report, saying there was no corroboration of the casualty figures.
Faure Gnassingbe, son of Togo's long-time leader Gnassingbe Eyadema was
The opposition alleged the polls were rigged and organised protests.
Some 38,000 people fled to neighbouring Benin and Ghana.
"The principal responsibility for the political violence and the violations of human rights [lay with] the state security apparatus," said the report, which followed a fact-finding mission to Togo.
President Faure Gnassingbe's father, Gnassingbe Eyadema, ruled Togo for 39 years before his death in February.
The army installed Mr Gnassingbe as president before international pressure persuaded him to contest elections.