The United Nations says the human rights situation in Burundi has deteriorated since current President Evariste Ndayishimiye took office last year.
UN investigators said conditions had worsened for opposition parties, journalists and civil society groups despite the easing of some restrictions.
They said opposition supporters have been detained, tortured and arrested.
Some have disappeared.
Mr Ndayishimiye pledged to end repression when he came to power last year following the sudden death of former President Pierre Nkurunziza.