At least 25 people, most of them women, were killed and about 49 were injured in a blast inside Cairo's Coptic Cathedral complex on Sunday.
A bomb exploded in the chapel as Sunday Mass was about to end. President Abdel Fatah al-Sissi said at the state funeral for the victims attended by hundreds of mourners that a suicide bomber carried out the attack. He identified the bomber as a 22-year-old man who wore an explosive vest which he detonated in the chapel. The Interior Ministry released a picture of the alleged suicide bomber.
Sissi said that four other suspects in the attack have been arrested.
Three days of mourning has been declared in the country.
Coptic Pope Tawadros II cut short a Greece tour and also conducted a private service for the family of the victims.
"This calamity is not against the church but against the homeland, [against] all of Egypt," Pope Tawadros said after the service. "We are in a lot pain because of this evil ... but we are pleased they passed away during prayers, this is the best time to die.. during this [holy] month."
Coptic Christians make up about 10 percent of the Egyptian population and are vulnerable to mob attacks triggered by blasphemy accusations and building permits for new churches.
"Egypt's government needs to ensure immediate protection for the Coptic community, especially during the upcoming Christmas holiday," Sarah Leah Whitson, Middle East and North Africa director at Human Rights Watch, said in a statement. "The victims deserve a credible, transparent investigation that brings the perpetrators to justice and is crucial for ending such attacks."
This is the second bombing attack in Cairo this month. Last week, a car bomb on the main road leading to Giza pyramids killed six policemen in the city. The attack was claimed by a militant group affiliated with Muslim Brotherhood.
In 2011, about 23 Christians were killed by a suicide bomber at a church in Alexandria.