According to a Voice of the Martyrs contact at least 20 were also injured in the attack in the Minya region, south of Cairo — the same place where two buses were attacked one year ago.
The bus was heading towards a local monastery, a senior Coptic cleric says.
The Islamic State group says it carried out the attack. Islamist militants have targeted Egypt’s Coptic Christian minority repeatedly in recent years.
Egypt’s Copts have in the past accused the authorities of making only token gestures to protect them from such attacks.
Egypt is a Muslim-majority country and its Christian minority – mostly members of the Coptic Orthodox Church – make up around 10% of the population.
Sources: BBC, Voice of the Martyrs