The United Nations has told Belgium to apologise for its colonial past and criticised its newly renovated Africa Museum for not doing enough to exorcise the demons of it exploitation of the Congo.

Filled with more than 180,000 looted items and 500 stuffed animals, the museum celebrated the Belgians, who turned the Congo into a slave state ruled by Leopold II, for more than a century. The king’s brutal regime, which inspired Joseph Conrad’s Heart of Darkness, killed millions and ruthlessly plundered the region of rubber.

After a week-long investigation, a UN working group said that racism suffered by those of African origin in Belgium could be traced back to the country’s failure to address its past. The panel noted the many remaining statues of Leopold and monuments to the colonial army that dot the streets and parks of Brussels.

“We urge the government to apologise for the atrocities committed during the colonisation," said group president Michal Balcherzak.

Charles Michel, Belgium’s prime minister, said he thought the findings, to be published in full in September, were “very strange”.

“We will have the opportunity to make our formal remarks. We certainly will,” he said and insisted Belgium stood against all forms of discrimination.