Amnesty International says Nigerian security forces have killed dozens of people during operations against separatists in the south-east of the country.
This comes after the government accused the banned Indigenous People of Biafra (Ipob) movement of attacking police stations killing dozens of officers.
Amnesty is calling for an impartial and open inquiry as well as fair trials for anyone accused of violence.
It says the evidence it has gathered in Imo, Anambra and Abia states paints a damning picture of ruthless excessive force by the Nigerian police and army.
As well as killing 115 suspected militants, the rights group says people were randomly picked up from their homes who had nothing to do with the attacks on police stations – some were tortured.
Ipob has denied any involvement in the violence.
Its leader Nnamdi Kanu is on trial for treason.
There is a danger that the authorities’ response to the unrest could fuel resentment and anger and lead to yet more violence in south-east Nigeria.