United Nations (UN) investigators say Venezuela's government has "committed egregious violations" amounting to crimes against humanity.
Cases of killings, torture, violence and disappearances were investigated in a fact-finding mission for the UN Human Rights Council.
The UN team said President Nicolás Maduro and other top officials were implicated.
Venezuela's UN ambassador has described the mission as a "hostile initiative".
Ambassador Jorge Valero said last year that the UN action was part of a US-led campaign. The UN team was blocked from travelling into the country.
Venezuela is suffering a severe economic and political crisis. Millions have fled in recent years.
What did the UN team say?
In the report of its findings on Wednesday, the UN team said Venezuela's security services had been engaged in a pattern of systematic violence since 2014, aimed at suppressing political opposition and generally terrorising the population.
Mr Maduro and the ministers of interior and defence were not only aware of the crimes, but gave orders, coordinated operations and supplied resources, the report said.
It called on Venezuela to hold those responsible to account and to prevent further violations from taking place.
"The Mission found reasonable grounds to believe that Venezuelan authorities and security forces have since 2014 planned and executed serious human rights violations, some of which – including arbitrary killings and the systematic use of torture – amount to crimes against humanity," the mission's chairperson, Marta Valiñas, said in a statement.
"Far from being isolated acts, these crimes were coordinated and committed pursuant to state policies, with the knowledge or direct support of commanding officers and senior government officials."
A typical operation might involve weapons being planted in an area thought to be loyal to the opposition, with security services then entering the area and shooting people at point blank range, or detaining them, torturing them, and killing them.
The report also looked into the violent response to opposition protests and the torture of people detained at them.
Investigators made their conclusions after looking into 223 cases. They said almost 3,000 others corroborated "patterns of violations and crimes".
The report will be presented to UN Human Rights Council member states next week, when Venezuela will have a chance to respond.
How significant are these findings?
Analysis by Imogen Foulkes, BBC News, Geneva
The UN team was not allowed to travel to Venezuela for this report. This is not unusual; Syria has never allowed the UN Read More – Source