A group of United Nations experts has said that Venezuela's presidential election lacked "basic transparency and integrity".

The UN panel of experts has echoed the criticism levelled by the Carter Center, whose independent observers said earlier that the election "could not be considered democratic".

Both organisations have criticised Venezuela's National Electoral Council (CNE) for declaring the incumbent, Nicolás Maduro, the winner without publishing detailed voting tallies.

The UN human rights chief had earlier warned of a "climate of fear" caused by arbitrary detentions carried out in the wake of the election.

According to the Venezuelan government, more than 2,400 people have been detained since 29 July - the day the disputed election result was announced.

UN Human Rights Chief Volker Türk said in a statement published on Tuesday that "it is especially troubling that so many people are being detained, accused or charged with incitement to hatred under counterterrorism legislation".

The UN denounced the fact that in the weeks since the vote, street protests and criticism on social media had been met with "fierce repression" by the state.

It said its independent rights experts had recorded 23 deaths between 28 July - when the election was held - and 8 August. Most of them were caused by gunfire.

Mr Maduro on Monday put the death toll at 25 and blamed "opposition violence" for the deaths.

He urged the justice system - which is largely under the control of his socialist PSUV party - to act with an "iron fist".

UN human rights chief Volker Türk insisted that all deaths be investigated and stressed there should be no repeat of the "disproportionate use of force by law enforcement officials and the attacks on demonstrators by armed individuals supporting the government".

Protests erupted after the CNE, which is dominated by government allies, declared Mr Maduro the winner without publishing detailed voting tallies.

The opposition says the tallies prove that its candidate, Edmundo González, won by a wide margin. It has uploaded copies collected by its observers on election night to the internet.

These tallies - which have been reviewed by independent observers and media - suggest Mr González won 67% of the vote, compared to Mr Maduro's 30%.

On Tuesday, a panel of UN experts invited by Venezuela's National Electoral Council to follow the election made its preliminary results public.

The experts found that the election day had taken place "in a largely peaceful environment" and was "logistically well organised".

But they concluded that the way the CNE had announced the results "fell short of the basic transparency and integrity measures that are essential to holding credible elections".

In particular, the UN experts highlighted the CNE's failure to publish "any results (or results broken down by polling stations), to support their oral announcement" declaring Mr Maduro the winner.

They said that this failure "had no precedent in contemporary democratic elections".

The UN panel also said it had reviewed a small sample of the voting tallies published by the opposition and found them to "exhibit all the security features of the original result protocols".

The government had earlier tried to cast doubt on the veracity of the voting tallies uploaded by the opposition, alleging that they lacked the necessary signatures and security features such as QR codes.

The Venezuelan foreign ministry has dismissed the UN experts' report has "a propaganda act serving the interests of the Venezuela far right".

Jorge Rodríguez, the head of government-dominated National Assembly, called the UN panel "fake experts" and "rubbish", and accused them of lying.

His proposal to change the electoral laws so that "no foreigner will ever be able to come to Venezuela to give an opinion on anything related to elections in Venezuela" was met with a standing ovation.