"This alarming violence is fuelled by the widespread impunity that prevails in Burundi," they warned.

Violations, they said, were happening with virtually no scrutiny in Burundi, where media and civil society face severe restrictions, the justice system is "dysfunctional", and in March, Burundi shut down the UN human rights office in Bujumbura.

In light of the dire lack of oversight in the country, the investigators argued that it was vital they be allowed to continue their work.

They will present their report on September 17 to the UN Human Rights Council, which will determine if their mandate will be renewed.