More than two dozen others were injured in the attack in Minya province
At least 28 people have been killed in Egypt after gunmen attacked buses carrying Coptic Christians.
It happened in Minya province, which is south of Cairo.
BBC reports that the group was travelling to a monastery when they were attacked.
No group immediately claimed responsibility for the attack, which left 25 others injured.
Bishop Makarios of the Coptic Orthodox Church told The New York Times that children, elderly people and workers were among the dead.
Egyptian Christians have been victims of violence on several occasions in recent years.
Last month, 46 people were killed after suicide bombers targeted churches in Tanta and Alexandria.
Islamic State claimed responsibility for the bombings.
President Abdul Fattah al-Sisi declared a three-month state of emergency after April's attacks.
Irish President Michael D Higgins expressed sympathies to the people of Egypt and victims' families "on behalf of the people of Ireland".
He said: "The attacks on the Coptic community in Egypt should be of concern to all members of the international community, and were among the issues that I highlighted when I was visited by His Holiness Pope Tawadros II earlier this month.
"I have conveyed my condolences to Pope Tawadros, to the Coptic community in Ireland, and to the Egyptian Ambassador in Ireland.”
In a statement, Foreign Affairs Minister Charlie Flanagan said he learned of today's attack with "great sadness".
“Just last week in Dublin, I offered my condolences to the Head of the Coptic Church, His Holiness Pope Tawadros II for last month’s attacks," Minister Flanagan said. "Today I again offer my sincere condolences to those killed and injured and their loved ones, as well as to the entire Coptic Christian community.
“I condemn in the strongest terms the actions of those responsible for this barbarous act of terrorism.”