"Abuses of protesters, including torture, were part of "the breakdown of the rule of law" in the South American OPEC member country", UN High Commissioner for Human Rights Zeid Ra'ad al-Hussein said in a statement.
Despite growing global criticism, Maduro has remained firm in pressing the constitutional assembly forward in executing his priorities.
Foreign ministers from 17 Western Hemisphere nations are condemning Venezuela's new constitutional assembly, saying their governments will refuse to recognize the all-powerful body.
The first vice president of the ANC Aristobulo Isturiz said this will help the country fight "the economic war that Venezuela is facing".
Also Tuesday, the Supreme Court ordered the arrest of the mayor of the district of Chacao, in Caracas, Ramon Muchacho, for not following an order to remove barricades during recent protests.
President Donald Trump's administration announced last week that it was freezing any US assets Maduro might possess and barring any American from doing business with him in response to the July 30 election for delegates to the constitutional assembly.
His next action could be to deprive of parliamentary immunity of certain opposition mps to send them to jail.
The situation became more acute with the installation of the Constituent Assembly last Friday, given that the body was not recognized by the Venezuelan opposition or by many governments and global organizations.
A further five nations participated in the meeting but didn't sign the document.
The opposition is struggling to regain its footing since last week's seating of a loyalist special assembly, which is now busy rewriting the country's constitution.
Leaders of congress, which previously voted not to recognise any of the new super-body's decrees, said lawmakers would try to meet in the gold-domed legislative palace Wednesday, but there were questions whether security officers guarding the building would let them in.
"We are chavistas until death", Maradona wrote on his official Facebook page on Monday night, using a term to refer to supporters of late former Venezuelan President Hugo Chavez.
Venezuela has been beset by a wave of anti-government protests since April 1 that have left at least 121 people dead.
Presenting the preliminary findings from an investigation conducted in June and July, the United Nations rights office described "a picture of widespread and systematic use of excessive force and arbitrary detentions against demonstrators in Venezuela".
Summoned by Peruvian president, Pedro Pablo Kuczynski, one of Maduro's most hardline critics, the meeting was held at the Foreign Ministry, and was chaired by Luna, although the Head of State did join the meeting in its final minutes.
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