"Witness accounts suggest that security forces ... have systematically used disproportionate force to instill fear, crush dissent and to prevent demonstrators from assembling, rallying and reaching public institutions to present petitions," the UN office said.
More than 120 people have died in protest-linked incidents since spring as critics accused leftist President Nicolas Maduro of illegitimately consolidating power, including stacking the Supreme Court with loyalists and holding an election for a new legislative assembly packed virtually with only his backers.
"The responsibility for the human rights violations we are recording lies at the highest levels of government," UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein said.
-- Security forces allegedly are responsible at least 46 deaths. Other, pro-government armed groups are accused of being responsible for 27 deaths. The UN report said it does not have details for all the deaths.
-- Some demonstrators have attacked security officers; eight officers have been killed during the demonstrations.
-- Pro-government armed groups "routinely break into protests on motorcycles, wielding firearms and harassing or in some cases shooting at people."
-- Security forces fired tear gas and buckshot and anti-regime demonstrators without warning. Several interviewees "said tear gas canisters were used at short range, and marbles, buckshot and nuts and bolts were used as ammunition."
-- More than 5,000 people have been arbitrarily detained, and more than 1,000 reportedly still are in detention.
-- In several cases, "there were credible reports of cruel, inhuman or degrading treatment by security forces of such detainees, amounting in several cases to torture" -- including electric shocks, beatings and threats of killings.
Venezuela's ministry of communication didn't immediately respond to CNN's request for comment about the UN report. Government officials have said anti-regime protesters were responsible for criminal violence fomented by opposition leaders.
The UN office said it interviewed 135 people -- including victims, their families and witnesses -- remotely from June 6 to July 31. Venezuelan authorities did not respond to the team's request for access, the office said.
"I call on all parties to work towards a solution to the rapidly worsening tensions in the country, to renounce the use of violence and to take steps towards meaningful political dialogue," Zeid said.
The UN report comes days after a controversial new legislature, the Constituent Assembly, took power.
The new assembly was created in a July 30 national vote orchestrated by Maduro and boycotted by the opposition.
Filled with Maduro supporters, it is expected to eventually take the place of the opposition-led National Assembly in a move that critics fear will erode democracy, and is expected to rewrite the Constitution at Maduro's behest.
Constituent Assembly leader Delcy Rodriguez said a "truth, justice and peace commission" will investigate the violence in the country in the past few months, and warned that "justice will come"
to some members of the opposition.
On Saturday, the Constituent Assembly unanimously fired Attorney General Luisa Ortega Diaz, a Maduro critic. The Supreme Court said she would be investigated for what it called serious violations and offenses.
Ortega has called the Constituent Assembly's election illegal, and said she would continue to be attorney general.
Both the Constituent Assembly and the National Assembly met Tuesday in separate chambers of the legislative palace in the capital, Caracas. That raised prospects that two camps may claim to be the country's legitimate government
Meanwhile, Venezuelan authorities say a manhunt is underway after an anti-government paramilitary attack at a military barracks
in the northwestern city of Valencia early Sunday.
Twenty people attacked the barracks; two were shot dead, one was injured and is recovering in a hospital and seven people were arrested, according to Minister of Communication Ernesto Villegas.
Ten others fled when the gunfight began, and are being hunted down.
Latin American foreign ministers meet
Most countries around the world have called the July 30 vote fraudulent and say the new assembly is a sign of a dictatorship.
The United States and other nations slapped sanctions on Maduro and other government officials after the vote.
Foreign ministers of 12 nations in the Americas met in Lima, Peru, on Tuesday to discuss the "critical situation in Venezuela" and to explore ways to achieve a "peaceful and negotiated" outcome. Among the countries represented were Argentina, Brazil, Canada and Mexico.
The ministers condemned the break of the democratic order in Venezuela and said their countries wouldn't recognize the Constituent Assembly. Only laws enacted by the National Assembly would be recognized.
The envoys also condemned what they said were Venezuela's systematic violations of human rights and denounced the Maduro government's incarceration of political figures.
The group called for new elections with international observers.
Months of strife
The Constituent Assembly's election follows months of sometimes deadly anti-regime protests and an economic crisis
that led many to leave the country
in search of easier access to food and medicine.
Maduro's opponents attempted to hold a referendum vote to remove him from office after they won a National Assembly majority in 2015, but the Supreme Court blocked all attempts to remove him.
The Supreme Court in late March attempted to dissolve the National Assembly, leading to the latest wave of unrest.