The killings come a day before the Coptic Church's Christmas, on January 7th. Security at churches is normally tightened in Egypt during this time. The attack happened in Minya, a city south of the country's capital Cairo.
A spokesman for Egypt's Interior Ministry has said the act was not based on religion, but on undermining security forces.
Hany Abdel Latif said: "(It) has nothing to do with any of the holidays of our Coptic brothers, it is instead aimed at the security forces, to try to undermine their resolve."
Around ten percent of Egypt's population are Coptic Christians, amounting to approximately 8.5 million people. Christians and Muslims have generally lived together peacefully in the country for hundreds of years.
The first democratically-elected president of Egypt, Mohammad Morsi, was removed from power by the military following nationwide protests last year.
Since then, a number of churches and Christian properties were burned and destroyed in south of the country, which is poorer and home to many believers.
Mohammad Morsi's party, the Muslim Brotherhood, denies any involvement in Christian persecution there, saying the army was using attacks on Christians as an excuse to employ a fierce security crackdown.
Muslim extremists based in the Sinai area of Egypt also started killing hundreds of soldiers and policeman after Morsi was ousted.