Another 25 people were wounded in the attack, which took place south of Cairo, Egypt's ministry of interior told the AP.
No group immediately claimed responsibility.
Coptic Christians make up just 10 percent of Egypt's population of 92 million.
Egypt responded to Friday's attack by launching airstrikes against what it said were militant training bases in eastern Libya, according to the AP. The bases targeted are associated with the Shura Council, an Islamist militia known to be linked to al-Qaeda. Egypt's president, Abdel Fattah el-Sisi, announced the retaliatory actions hours after the attack.
Trump said the attack "steels our resolve to bring nations together for the righteous purpose of crushing the evil organization of terror, and exposing their depraved, twisted and thuggish ideology."
ABC News' Julia Jacobo and Jordyn Phelps contributed to this report