Seven people have been shot dead and two girls allegedly raped in what is believed to be a revenge attack on a secondary school in northern Kenya.

Gunmen killed six children and one security guard in the dawn attack on Saturday which is thought to have been led by a former pupil suspended for fighting, a Kenyan police official said.

The suspected ringleader, a senior at the Lokichogio Mixed Secondary School, had vowed to take revenge after his punishment last week, according to Gideon Kibunja, Rift Valley regional criminal investigations chief, covering the Turkana region where the attack took place.

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Kibunja said the gunmen, believed to be from neighbouring South Sudan, were looking for the head teacher of the school and the other student involved in the fight that led to the ringleader's suspension. The gunmen then shot other students in frustration at not finding the pair, he added.

The suspended student was arrested later on Saturday, but was killed when a mob of angry residents overwhelmed the police and took hold of him, Kibunja said.

Kenya’s KTN television channel said the victims included four boys and two girls and witnesses say the gunmen raped two girls and injured another 18 students, according to the BBC.

Clashes over cattle grazing and farming land are relatively common among communities in the north of Kenya and often result in revenge attacks.

Turkana county borders war-torn South Sudan and arms smuggling is a common problem along the border with police having little control over the weaponry being brought in.

“The attack ... is a painful reminder of the state of insecurity along the border," Josphat Nanok, Turkana county's governor, said on Twitter.

There has been a wave of violent incidents taking place in schools along Kenya’s border areas over the past two years.