A human rights group has accused Cameroon's security forces of numerous abuses against civilians in the struggle against Boko Haram and said 50 people who rounded up for questioning later died.

“We cannot in the name of the fight against Boko Haram, which is already tough, allow people to be petrified and terrorised by those who are supposed to protect them,” said Maximilienne Ngo Mbe, head of Cameroonian association REDHAC.

Her group said the army has used intimidation and torture in an effort to extract intelligence from locals that can be used against Nigeria-based Boko Haram fighters.

The militants have extended their brutal six-year insurgency to Niger, Chad and Cameroon, drawing a regional response to the group's bloody campaign. The conflict has already killed 13,000 people since 2009.

In noting the state's alleged abuses, Ngo Mbe told of around 50 people who suffocated recently while locked in a cell after being rounded up for questioning from two villages in far northern Cameroon.

The victims, she said, were subsequently buried in a mass grave in the bush, but did not provide any further details.

A spokesman for Cameroon's army told AFP: “We have no comment to make. The NGOs have their role. We have nothing to say.”

Ngo Mbe's group said far northern Cameroon has become a zone of numerous right violations as locals have become trapped between militants and the government.

“Army soldiers commit abuses on residents while disregarding international human rights,” she told reporters on Wednesday.

On Monday, a Cameroonian military officer said more than 1,000 suspected Boko Haram fighters were being held in Maroua at a prison in the country's far north.

Nigeria's military has also been accused of major abuses in the fight against Boko Haram.