A woman and her two children aged two and eight were shot dead by raiders in a remote village in Merti sub-county, Isiolo.
The Saturday attack at Dogogicha location took place at around 5.30am.
A neighbour who stepped outside to look for his stolen donkeys was also killed.
The woman succumbed to the multiple gunshot wounds while under treatment at Merti Sub-county Hospital. Isiolo County Commissioner Geoffrey Omading said the attack took place at Aliomatuma village near Merti township.
Police are looking for the suspects in Wajir West, Eldas, Laisamis, Saku and North Horr.
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Mr Omading said about 1,000 livestock were stolen in the raid. "The initial probe shows the raiders' intention was to steal but sadly they killed young children and their mother," he said. Mr Omading added: "We have enough security in Merti and the neighbouring Marsabit and Wajir counties." Ten days ago five people were killed in the same area.
Over two years, more than 100 people have been killed in Merti sub-county locations of Kom, Biliqo, Bassa and Yamicha.
Isiolo leaders were unanimous in condemning the latest killings. Jubilee governor aspirant Abdi Guyo, his ODM counterpart former EACC boss Halake Waqo and Woman Representative hopeful Mumina Gollo together with former Isiolo North MP Joseph Samal appealed to Interior CS Fred Matiang'i to address the insecurity situation in Isiolo county.
Leaders from Isiolo have in the past decried the increasing insecurity in the county that has led to the loss of lives and livestock.
Addressing the media in Nairobi last week, they said there have been several attacks in the last month. They claimed the attacks seem to be coordinated in the neighbouring counties.