Bonaya Godana, the member of parliament for North Horr district in which the attack took place, told journalists that 56 Gabra-clan villagers, most of them young children and their mothers, had been killed in Tuesday's raid on Turbi village.
Police said earlier that 10 of the Borana-clan attackers had also been killed. But a Catholic church missionary reported on Wednesday that a further 10 Borana tribesmen had also been killed in an apparent revenge attack.
Godana, a former Kenyan foreign minister, who was touring the scene of the brutal attacks, said many of the initial victims had been shot dead while preparing to go to school.
"As of this morning, 56 of our people have been confirmed dead and of them are 22 schoolchildren, and most of them died in their school uniforms," he said, adding that 10 schoolchildren were among those seriously wounded in the attack.
"The majority of the dead are mothers and their children," Godana said. "Three other people are still missing and we suspect that they are dead."
But a Catholic Church official said 10 Borana clansmen, including four children, had also been killed on Wednesday.
"Six adults and four children were taken from a vehicle that was being driven by a priest and killed them with crude weapons around noon yesterday," the source said.
"They were Boranas so this appears to be a revenge attack," he said, and added the attackers used crude weapons and spoke the Gabra language. The priest was left unharmed.
The revenge attack occurred near the northern Kenyan town of Sololo, about 30km north of Turbi.
Police, who have deployed in large numbers in the region to catch the village attackers and forestall possible revenge attacks, had no immediate comment on the latest killings.
The two clans have feuded persistently over water and pasture in the semi-arid region.
Alexander Abduba, a Gabra clan elder, was reported as saying the initial attack was part of a plan by the Borana to take control of Turbi, an oasis in the parched region.
"The Borana want to force the Gabra out," he said. "Turbi is a watering point, a pasture land for animals in the desert. They want to take over watering points and pasture lands.
"They want to extend the Borana area of control into Gabra land," Abduba said. "It is basically an expansion programme."
No members of the Borana tribe have made a public statement on either one of the attacks.