Ilaria Allegrozzi, Human Rights Watch's senior central Africa researcher, said in a report "Armed separatist groups are kidnapping, terrorizing, and killing civilians across the English-speaking regions with no apparent fear of being held to account by either their own leaders or Cameroonian law enforcement."
The rights watchdog said rebels had killed at least seven people, injured six more, raped a girl and kidnapped as many as 82 people since January "in an uptick of violence."
The separatists have targeted schools, torching at least two facilities, and attacked a university, it said.
The allegations are based on interviews with several dozen victims and witnesses as well as medical records and visual evidence, HRW said.
On June 1, soldiers in the Northwest Region killed nine civilians, including a baby, the defense ministry said, describing the deaths as a "grave and unfortunate incident."
A conflict in Cameroon's Northwest Region and Southwest Region has raged for nearly five years, pitching government forces against anglophones campaigning to secede from the majority French-speaking state.
In 2017, mounting anglophone resentment at perceived discrimination snowballed into the declaration of an independent state -- the "Federal Republic of Ambazonia," an entity that is not recognised internationally.
The country's veteran president Paul Biya, 89, who has ruled with an iron fist for nearly 40 years, responded with a crackdown.
The violence has claimed more than 6,000 lives and displaced around a million people, according to the International Crisis Group (ICG) think tank.
The UN and international NGOs have accused both sides of human rights abuses.
HRW renewed this allegation, saying government troops had committed rights violations including "extensive burning of villages, homes, and shops, killings, torture, mistreatment, incommunicado detention and rape of civilians."