Geneva (AFP) - The UN warned Friday that serious rights violations were continuing in Nicaragua with impunity, urging the country to overhaul its security sector and to promptly investigate all abuse allegations.

In a fresh report, UN human rights chief Michelle Bachelet and her office detailed a wide range of violations committed in Nicaragua since April 2018, when a opposition protests mushroomed into a popular uprising that was met with a brutal crackdown.

More than 300 people were killed, some 2,000 injured and some 800 were imprisoned at the height of the crisis, which prompted more than 80,000 people to flee the country, according to UN numbers.

Rights investigators have "documented gross human rights violations committed since mid-April 2018 in the context of the protests," the report said.

It pointed among other things to disproportionate use of force by police, which in some cases resulted in extrajudicial killings, violence by pro-government armed groups, arbitrary detention, sexual violence and torture.

In the report, Bachelet said that Nicaraguan authorities had failed to investigate abuse allegations and to bring perpetrators to justice.

"This situation reflects a lack of will to ensure accountability and entrenches impunity for human rights violations," the report said, warning that this denies victims' right to justice, and also "erodes public trust in state institutions".

Bachelet's office was not permitted access to the country to conduct its investigation, and based the report findings on nearly 200 interviews, as well as documents and video and photo images.

The situation in Nicaragua has calmed some after the powerful Catholic Church brokered several rounds of peace talks between President Daniel Ortega and opposition groups.

The government in February also began the staggered release of prisoners into house arrest, and by June 11 had released nearly 492 prisoners.

But talks with the government have stalled, notably due to Ortega's rejection of a key demand that he resign and bring forward elections slated for 2021.

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- 'Criminalised dissent' -

According to Friday's report, which Bachelet will present to the Human Rights Council in Geneva next week, there has been a "continued and notable reduction of civic space" in the country.

The country late last year expelled two international human rights missions, and also withdrawn legal registration from a number of prominent civil society organisations, and the report also pointed to continued attacks on journalists, students and other activists.

As of July, some 100 journalists had fled the country, it said.

At the same time, it said "arbitrary arrests and detentions continued to be used as a means to repress the expression of dissent, and instances of torture and ill-treatment targeting persons deprived of liberty in relation to the protests persisted".

Far from investigating allegations of abuse, Nicaragua's justice system had been used to "criminalise dissent and to ensure impunity for those responsible," the report said, decrying a "lack of independence of the judiciary from the executive."

The report called for the government to conduct "prompt, thorough and transparent criminal investigations and prosecutions into all allegations of human rights violations."

It also called for the "dismantlement and disarmament of pro-government armed elements and comprehensive reform of the security sector" in the country, insisting that officers should undergo "human rights vetting" and be under civilian supervision and oversight.

The report also called for Nicaragua to promptly resume cooperation with Bachelet's office, and urged the rights council to step up its monitoring of the rights situation in the country.