GENEVA (Reuters) - U.N. human rights chief Michelle Bachelet expressed outrage on Thursday at comments by Burundi’s ambassador in New York comparing the chairman of a U.N. inquiry into the country to a participant in the slave trade.

United Nations High Commissioner for Human Rights Michelle Bachelet attends an ACANU briefing in Geneva, Switzerland, September 20, 2018. REUTERS/Denis Balibouse

Burundi’s Ambassador to the United Nations Albert Shingiro, speaking at the U.N. General Assembly on Wednesday, rubbished a report by the Commission of Inquiry into human rights in Burundi.

His government has already criticized the report several times and refused to cooperate with the investigators.

According to a transcript posted on the Burundian mission’s website, tweeted by Shingiro, he called the commission’s Senegalese chairman Doudou Diène “an African tasked with selling another African country at auction”.

“Unfortunately it’s not the first time that it’s happened, we saw Africans selling other Africans during the era of slavery and colonialism,” Shingiro added.

Bachelet said in a statement his “comments were “deeply regrettable in both tone and substance”.

The Commission of Inquiry led by Diène was set up in 2016 and published a detailed 272-page report earlier this year that said Burundi’s government and its supporters were responsible for crimes against humanity.

Burundi has called the report “lies” and threatened to sue its critics, including the three commissioners.

“The threat to prosecute the members of the Commission for the work they have done at the express request of the Council – a subsidiary body of the General Assembly - is unacceptable and should be immediately withdrawn,” Bachelet said.

“And the personal attack on the Chair of the Commission of Inquiry, Mr Doudou Diène, comparing him to a participant in the slave trade, was a disgrace,” she added.

“Burundi’s belligerent and defamatory response to the findings of the Commission of Inquiry, and its repeated and wholly unsupported assertions that the Commission was the puppet of mysterious external forces, as well as the Government’s complete failure to address the very serious findings of the Commission of Inquiry, are reprehensible.”