The ruling regime in Eritrea is generally held to be one of the worst human rights abusers in the world. Eritreans fleeing oppression account for a large proportion of migrants seeking refuge in Europe. But on Friday, barring an unexpected shift, Eritrea will be elected a member of the UN’s top human rights body, the human rights council, by a vote in the UN general assembly.

The voting will also confer council membership on five other countries – Bahrain, Bangladesh, Cameroon, the Philippines and Somalia – that independent advocacy groups also judge to be “unqualified” by reason of their chronic human rights abuses and negative voting record on rights issues.

The groups – UN Watch, the Human Rights Foundation and the Raoul Wallenberg Centre for Human Rights – warned the results could severely undermine the council’s credibility.

The outcome of the voting can be predicted in advance because the geographically organised regional slates, to which Eritrea and the other countries belong, have not nominated alternative candidates, so all six will be elected unopposed. Attempts last year by the EU and the US to make the process more competitive failed. Citing this among other reasons, the Trump administration withdrew from the council in June.

In a report this week, Irwin Cotler, the head of the Raoul Wallenberg Centre for Human Rights and a former Canadian minister of justice, said: “Regrettably, when the UN itself ends up electing human rights violators to the human rights council, it indulges the very culture of impunity it is supposed to combat. The world’s democracies must join in the preservation and protection of the council’s mandate and not end up accomplices to its breach.”

Hillel Neuer, the executive director of UN Watch in Geneva, said the creation of the council in 2006 by the late Kofi Annan, then UN secretary general, was intended to weed out the worst abusers, whose presence had discredited the council’s predecessor, the now-defunct UN human rights commission. “Sadly, this was never respected ... This year, there is not even the illusion of competition,” Neuer said.

The report also raised doubts about four other candidates in Friday’s elections, when 18 new countries will join the 47-member council for three-year terms. Burkina Faso, Fiji, India and Togo all had “questionable” credentials, it said. Current members include Saudi Arabia and China. Both have recently come under fire for serious abuses, including abduction and mass detentions.

The report urged the 193-member general assembly to reject known rights abusers. “UN member states have the legal right – and moral obligation – to refrain from voting for unqualified candidates,” it said. Such appeals have been ignored in the past. In recent elections, China received 180 votes and Saudi Arabia 154.

Critics of the process fear Eritrea’s elevation will give undeserved respectability to the authoritarian regime of the president Isaias Afwerki, which has an exceptionally grim record of executions, enforced disappearances, torture, arbitrary arrest and detention, and draconian restrictions on civil rights and media freedom.

The Obama administration, which joined the HRC in 2009, accepted the council had an important role to play in monitoring observance of UN resolutions and human rights treaties, but its argument that council membership encouraged countries to reform was not borne out by subsequent experience.

The Trump administration said its decision to quit was prompted by the presence of serial human rights abusers and a lack of competitive elections. Nikki Haley, the outgoing US ambassador to the UN, called it “a cesspool of political bias”.

The US’s decision was also prompted by Donald Trump’s anger at sharp UN criticism of his administration’s human rights record, in particular its mistreatment of migrant families at the US-Mexico border, and at the HRC’s perceived hostility towards Israel.

In a statement, Neuer expressed disappointment that EU countries were not doing more to support the council after the US boycott. “By turning a blind eye as human rights violators easily join and subvert the council, leading democracies will be complicit in the world body’s moral decline,” he said. “We need to hear the EU’s [foreign policy chief] Federica Mogherini and EU member states lead the call to oppose the worst abusers. So far, they have been silent.”