Northeastern Regional Commissioner John Otieno confirmed the incident on Wednesday evening, saying the deceased were ambushed and killed by unknown gunmen while they were inside their vehicle.
"We have launched investigations to establish the cause of the incident. The police have already arrested one suspect who is aiding with investigations," Otieno told journalists.
Otieno said the attack is suspected to be a revenge mission after another person from the rival clan was murdered.
He added that at least 10 people from either clan have been killed in the inter-clan clashes said to have been caused by a longstanding land scuffle. Residents said two of the victims of the attack were school students who were on their way home for a holiday.
"The six people who were killed were traveling in a vehicle but were stopped along by the attackers and all of them were executed, including two high-school students who were going home for the holiday," a local resident who declined to be identified said on phone.
Tension remained high amid fears of retaliation from the affected group. Inter-clan clashes over pieces of land are common in Garissa County, with several people losing their lives and scores getting injured as a result.
Residents said the loss of communal grazing land to farming and environmental degradation has also fuelled conflicts in a number of pastoral areas across northern Kenya, noting that freedom of movement over large areas was a crucial element of the pastoralists’ dry lands resource management system.