Police in Naivasha have arrested a man who cut his two-year-old step-son's genitals after he urinated in the basin while being washed.

The man, who has been married to the boy's mother for two months, committed the beastly act after he warned the child against urinating in the trough.

He was rescued by police from angry residents of Gatamaiyu village who bayed for his blood after the boy's mother sounded an alarm.

The mother was preparing lunch at the time so she asked the man to clean the child.

Patrick Njoroge, an elder, said on Thursday that the suspect warned the boy before grabbing a knife and cutting part of his genitals.

Njoroge said the suspect also bit several parts of the minor's body before he was rescued by the mother who alerted neighbours.

"This is the most inhumane act we have seen in this village in years. The residents wanted to lynch the suspect but police arrived in time and took him to the station."

He noted the man was of sound mind and had never had any confrontations with villagers.

Esther Njeri, a children's rights activist, condemned the incident and asked police to ensure the suspect is penalised heavily.

The former nominated MCA said the minor was taken to Naivasha sub-county hospital and was responding well to treatment.

"Stern action must be taken against the suspect. We will follow the matter to its logical conclusion so the innocent minor gets justice."