Two people were killed and at least seven houses burnt when members of the banned Mungiki sect rampaged through a village during the funeral of a sect follower.
Farm animals were also slaughtered and shops raided when the followers, arriving for the burial, attacked anyone in sight without provocation.
The raid on Karia Village in Githunguri was in revenge for the death of the youth they had come to bury.
Administration Policemen shot dead one of the mob after the gang hacked to death a carpenter, Mr Lucas Kihiu Wahogo, at his workshop.
The Mungiki raiders were on their way to bury 17-year-old Joseph Kuria Ndung'u who had been killed by Karia villagers during an earlier raid when they cornered him then stoned him to death before burning his body.
The Mungiki men had then vowed to wipe out everyone in the village, witnesses said.
Trouble started yesterday when about 500 Mungiki followers were driven into the village on their way to the funeral, planned at nearby Gitito, the home of the youth's father.
The hearse was escorted by Mungiki members in two buses, five minibuses, more than 15 commuter taxis (matatus) and several other vehicles.
His family, which had prepared for the burial, was waiting for the body to arrive when chaos broke out.
As the cortege pulled into the village, the followers leapt out of the vehicles brandishing swords, machettes, pick-axes and clubs and descended on Karia trading centre.
Without provocation, they set upon the unsuspecting villagers before looting shops.
They slashed and bludgeoned anyone in sight and destroyed an unknown amount of property.
Seventeen-year-old Janet Wanjira who was at her home was hit on the head with a piece of wood, collapsed and was taken unconscious to Karia Mama Ngina Health Centre before being transferred to Kiambu district hospital.
The Mungiki man who was shot was carried away by his colleagues who put him in one of their vehicles.
The hour-long reign of terror ended only when Administration Police repulsed the raiders who regrouped and drove off for the burial.
At Gitito, the service was conducted according to Mungiki rites as police stood watch at access roads and at the market centre.
While the burial was taking place, some of the raiders who had infiltrated the village started setting houses ablaze, looting property and causing mayhem.
Villagers ran from their homes and hid in adjoining coffee plantations.
"They killed my brother's cows and stole all household items before burning his house," one terrified resident said.
"The violence brings to mind the gangs which used to roam the entire district in groups of 50 or a 100 terrorising residents just before the 1997 elections," another terrified resident said.
Police who were told of the attack and who could see smoke rising from the burning homes dismissed reports of the raid, saying the smoke was from charcoal burners.
The Mungiki youths had entered the village singing traditional war songs before running amok, attacking anyone in sight, torching houses and killing farm animals.
They threatened to wipe out all the residents to avenge the death of their colleague who was killed by villagers themselves avenging an earlier Mungiki attack.
The series of raids began two weeks ago when Mungiki youths attacked revellers at midnight in a local bar, using machettes and clubs, injuring eight of them. Two of the injured are still recovering in hospital from deep cuts.
Three days after that attack, 20 sect followers who are well known to the villagers since they come from the same area, began another indiscriminate attack on the villagers.
One of them — the 17-year-old they buried yesterday - was then killed by outraged villagers .
Witnesses said the group then swore to wipe out everybody in the village.
The two deaths yesterday were confirmed by Kiambu CID boss Paul Ndambuki.
Kiambu police boss Atanasius Munyagia said the Mungiki attackers now lived in Nairobi. Last week he had arranged to ambush them but the villagers he had lined up to help identify them arrived armed to the teeth and he had to postpone the ambush.