A United Nations human rights investigator has accused Rwandan-backed rebels in the Democratic Republic of Congo of killing more than 150 people last week.

Asma Jahangir says she has gathered overwhelming evidence that a massacre occurred in Kisangani on May 14.

She says rebels from the Congolese Rally for Democracy (RDC), who control the eastern Congo, carried out extrajudicial killings of civilians, soldiers and police officers in response to an attempted rebellion in the region.

People were shot, stabbed and hacked to death. She says some had their bodies ripped open, filled with stones and thrown into the river to sink.

Jahangir calls the killings "grave human rights violations."

It's not that the authorities have by mistake killed one or two people and they can explain it away," she says. "This is indefensible."

Jahangir says the killings took place after mutineers occupied a radio station in Kisangani and called for an uprising.

She says a crowd that gathered in the centre of the city killed six people, but the majority of the murders were carried out by rebel forces.

Rebel leaders deny responsible for the massacre and accuse the UN officials of siding with the RCD's enemies.