Kenyans are demanding justice after three men accused of brutally gang raping a school girl and dumping her in a pit latrine were ordered to cut grass as punishment.

The ferocious attack and lack of action towards those who carried it out has sparked outrage and deep anger.

The 16-year old girl was reportedly attacked, beaten and then raped by six men as she returned from her grandfather's funeral in western Kenya in June, before the gang dumped her, bleeding and unconscious, in a deep sewage ditch.

The victim knew some of the attackers, and three of them were taken by villagers to the local police station, The Nation newspaper said.

"The three...were only ordered to cut grass around the police camp and set free shortly after," the girl's mother told the paper.

She is now wheelchair-bound with a broken back, caused either by the beating or by being hurled down into the pit.

She has also suffered a fistula -- a hole between her vagina and rectum -- meaning she leaks stools and urine, the paper said.

"My wish is to see justice done," the girl told the Nation. "I want my attackers arrested and punished."

The newspaper has launched a campaign to raise money for the girl's medical costs, estimated at more than $7,000 (5,200 euros), a fortune for the family.

"Not only did she suffer a brutal crime that changed her life forever, she was also denied justice," said Ann Gitao-Kinyua, a senior manager from The Nation newspaper.

Lawmakers have condemned the attack and subsequent police failures, ordering action to be taken.

"This is despicable. Everyone involved should be taken to court - the rapists, and the police who recorded it as an assault and ordered these people to cut grass," said one comment on the newspaper's site.

"It is outrageous, what type of Kenya are we living in!," said another angry Kenyan in a message posted on social media.