Burundi on Monday barred three United Nations rights experts who had accused the government in Bujumbura of being responsible for abuses and warned of a danger of genocide from the violence.

In a letter sent by Foreign Minister Alain Aime Nyamitwe and seen by AFP, the Burundian government said the three UN investigators were declared persona non grata with immediate effect.

Pablo de Greiff from Colombia, Christof Heyns from South Africa and Maya Sahli-Fadel of Algeria had been appointed in December to lead the independent probe.

UN spokesman Stephane Dujarric expressed disapproval of Burundi's decision.

"It's critical that Burundi and every other country cooperate fully with UN human rights mechanism and that is including working with those representing it," he said.

The decision to bar the three UN experts came just days after Burundi announced plans to withdraw from the International Criminal Court, warning of a "plot" to harm the country.

The three experts had concluded in a report released last month that "gross human rights violations have and are taking place, committed primarily by state agents and those linked to them."

Thousands of people have been tortured, suffered sexual abuse or disappeared, while arbitrary detention has happened "on a massive scale", the report said.

UN diplomats said the move was clearly an angry response from Bujumbura to the report which paved the way to a UN decision to set up a formal Commission of Inquiry.

PULL OUT OF ICC

Burundi on Friday said it would pull out of the ICC amid fears that members of the leadership could be indicted as a result of the commission of inquiry's work.

Last week, a representative of the non-governmental organisation Trial International was stripped of her visa and ordered to leave Burundi.

The employee was scheduled to provide legal training to Burundian lawyers defending victims of state-sponsored violence.

Burundi has been in turmoil since President Pierre Nkurunziza announced plans in April last year to run for a third term, which he went on to win.

More than 500 people have died, many of them in extrajudicial killings blamed on Burundian police, security forces and militias linked to the ruling party, according to the United Nations.

At least 270,000 people have fled the country.

The UN Security Council is due to discuss the crisis in Burundi on Thursday and hear a report from envoy Jamal Benomar.

Heavily armed police patrol a street in Bujumbura, Burundi, on April 12, 2016.