NAIROBI, Kenya (AP) — Gunmen shot dead seven people, including six students, in a raid on a high school early Saturday that appeared to be a revenge attack by a student who had been suspended for fighting, a Kenya police official said.

The shooting occurred at dawn at Lokichogio Mixed Secondary School near the countries' border, Rift Valley regional criminal investigations chief Gideon Kibunja said. The attackers were thought to be from neighboring South Sudan.

A key suspect was a senior at the school who was suspended last week after he was found fighting and vowed to take revenge, Kibunja said.

The gunmen were looking for the school's principal and the student involved in the fight but couldn't find them, so they shot other students out of frustration, he said.

The suspended student was arrested later Saturday, but Kibunja said angry members of the public overwhelmed police and killed him.

The shooting comes a month after a high school girl was charged with murdering nine of her colleagues in a fire at a Nairobi boarding school.

Kenya's border areas are littered with firearms from neighboring countries that have experienced war, including South Sudan and Somalia. High schools have experienced a wave of violent incidents in the past two years.