Burundi has forced the United Nations to shut its local human rights office after 23 years, U.N. High Commissioner for Human Rights Michelle Bachelet said on Tuesday.

Bachelet said the central African state's government had declared it had made sufficient progress in human rights, so that the existence of the U.N. office was no longer justified.

“It is with deep regret that we have had to close our office in Burundi after a 23-year presence in the country,” she said in a statement.

Many advancements in human rights in Burundi had been jeopardised since 2015, when President Pierre Nkurunziza announced he would seek a third term, Bachelet added.

Violence surged after the announcement, which many saw as a breach of the constitution.

He won re-election but the decision to stand sparked protests and a security crackdown that left hundreds dead and prompted around half million to flee abroad.

In October 2016, Burundi suspended all cooperation with the U.N. office in Burundi, following publication of a report by a U.N. independent investigation that said the government and its supporters were responsible for crimes against humanity.

Burundi said the report was "lies" and when the U.N. Human Rights Council considered renewing the investigation in 2017, Burundi offered to accept U.N. human rights experts instead.

But the rights council voted both to renew the investigation and to send the experts, infuriating the Bujumbura government.

Burundi subsequently threatened to prosecute the rights council's team of investigators and accused its chairman of "selling" Africans like in the era of slavery, a comment that outraged Bachelet.

The government also threw out the three visiting U.N. human rights experts it had promised to cooperate with, accusing them of arriving unannounced and acting like spies.