The UN sought to extend the envoy's mission by a year despite a positive change on the part of new President Evariste Ndayishimiye.
Officially the country has reported only 170 cases and one death in two months.
Opposition Leader Agathon Rwasa of the National Liberation Forces party petitioned court last week seeking to nullify General Ndayishimiye's 69% victory.
FNL leader Agathon Rwasa in a challenge Thursday that there was significant evidence of fraud after the Election Commission announced on Monday.
He was not known to many East Africans until late last year, when he was rumored to be the anointed successor of outgoing President Pierre Nkurunziza.