A panel of experts from the United Nations said Venezuela’s recent presidential elections lacked “basic transparency and integrity,” adding an important voice to those who have cast doubt on President Nicolás Maduro’s claim he won the contest.

A four-member team sent by U.N. Secretary General António Guterres was in Caracas for over a month in the run up to the July 28 election, one of the few independent outside observers invited by Maduro’s government.

While the U.N. group praised the logistic organization of the voting, it harshly criticized the National Electoral Council, or CNE, for flouting local rules and announcing Maduro the winner without tabulated results from each of the 30,000 polling booths nationwide, something it said “had no precedent in contemporary democratic elections.”

“This had a negative impact on confidence in the outcome announced by the CNE among a large part of the Venezuelan electorate,” the U.N. experts said in a statement late Tuesday.

The U.N. statement follows criticism by another invited observer, the Atlanta-based Carter Center, which said it could not verify the CNE’s results. Venezuela’s foreign minister has blasted the Carter Center, accusing it of lying and servings as a tool of U.S. “imperialism.”

While the U.N. team stopped short of validating claims by the opposition that its candidate, former diplomat Edmundo González, trounced Maduro by a more than 2-to-1 margin, it said that the voting records the anti-Maduro coalition published online appeared to exhibit all of the original security features.

“This suggests a key transparency safeguard may be available, as intended, with respect to any officially released results,” the experts added, noting that electoral authorities failed to meet with the group prior to the mission’s departure from Venezuela five days after voting.

Since the election, security forces have arrested more than 2,000 people for demonstrating against Maduro or casting doubt on his claims that he won a third term.

Separately on Tuesday, the U.N.'s top human rights official expressed concern over the arbitrary detentions and “disproportionate use of force” in Venezuela as part of the crackdown.

“It is especially troubling that so many people are being detained, accused or charged either with incitement to hatred or under counterterrorism legislation,” U.N. High Commissioner for Human Rights Volker Türk said in a statement. “Criminal law must never be used to limit unduly the rights to freedom of expression, peaceful assembly and association.”

Türk’s comments come as Venezuela’s opposition gears up for a demonstration Saturday that it hopes will increase pressure on Maduro to recognize defeat and negotiate a political transition.

“If Maduro makes a realistic evaluation of his options, he’ll understand that digging in is not sustainable,” opposition leader María Corina Machado told journalists Tuesday.

Machado, who anointed previously unknown retired diplomat Edmundo González as her stand-in once she was banned from running in the presidential campaign, spoke to journalists at a virtual press conference from an undisclosed location due to safety concerns.

In her comments, she tried to temper expectations for a quick resolution of the political crisis.

“Nobody knows how long it will take, but without a doubt there are painful days that await us,” Machado said.

The U.N. human rights office said that in most of the cases it has documented, detainees haven’t been allowed to appoint lawyers of their choice or have contact with their families. “Some of these cases would amount to enforced disappearances,” it said.

Türk called for “the immediate release of everyone who has been arbitrarily detained, and for fair trial guarantees for all detainees.” He added that “the disproportionate use of force by law enforcement officials and the attacks on demonstrators by armed individuals supporting the government, some resulting in deaths, must not be repeated.”

Türk also noted there have been reports of violence against public officials and public buildings by some demonstrators and said violence is never the answer.

On Monday, International Criminal Court prosecutors said they are “actively monitoring” events in Venezuela.