Geneva - The Islamist militant group Boko Haram could be responsible for crimes against humanity in Nigeria, the UN said on Friday.
The High Commissioner for Human Rights is "extremely concerned" by the recent attacks on churches in Kaduna province and "tit-for-tat" reprisals by Christians which since 17 June have left more than 100 people dead, said Rupert Colville, spokesperson for the Office of the High Commissioner for Human Rights (OHCHR).
Boko Haram has said it was behind the attacks.
"Members of Boko Haram ... if judged to have committed widespread or systematic attacks against a civilian population - including on grounds such as religion or ethnicity - are likely to be found guilty of crimes against humanity," said Colville.
"Deliberate acts leading to population 'cleansing' on grounds of religion or ethnicity could also amount to a crime against humanity," he said.
The group is also blamed for bomb and gun attacks, mainly in Nigeria's north-east, that have claimed more than 1 000 lives since mid-2009.
The sect's attacks have grown increasingly sophisticated and have spread from the group's base in the northeast across the wider north and down to the capital Abuja, in the centre of the country.
It claimed responsibility for a suicide bombing of UN headquarters in Abuja in August that killed at least 25 people and a suicide attack on the Abuja office of one of the country's most prominent newspapers.
Its deadliest attack yet occurred in the northern city of Kano in January, when at least 185 people died in coordinated bombings and shootings.