The United Nations human rights chief says with "deep regret" that Burundi's government has forced the rights office in the troubled East African nation to close after 23 years.

Burundi in December asked the U.N. office to leave, months after the outgoing U.N. rights chief called the country one of the "most prolific slaughterhouses of humans in recent times."

New rights chief Michelle Bachelet says in a statement on Tuesday that human rights gains in Burundi have been "seriously jeopardized" since 2015. That is when President Pierre Nkurunziza announced he would run for another, disputed term, leading to months of violence that killed more than 1,200 people.

Burundi has been pulling back from international criticism, making history in 2017 as the first country to withdraw from the International Criminal Court.