Burundi's attorney general has acknowledged that the government buried dozens of suspected rebels who died in December attacks on three military bases without notifying their families, but fell short of admitting the existence of mass graves.

Human Rights groups accused the Burundi government of trying hide the extent of the killings during December 11 attacks by suspect rebels by burying bodies in mass graves.

Valentin Bagorikunda said Thursday that out of 87 people who died, the government buried 58 bodies of suspected rebels. Eight of those killed in the December 11 attacks were security officials, he says.

At least 400 people have died in Burundi since April when President Pierre Nkurunziza launched his campaign for a third term in office which many oppose. Nkurunziza was re-elected in July.