Cairo, Egypt, Dec 11, 2016 / 02:47 pm (CNA/EWTN News).- At least 25 persons were killed Sunday when a bomb exploded at a chapel attached to St. Mark's Coptic Orthodox Cathedral in Cairo, and dozens more were injured.

“Vicious terrorism is being waged against the country's Copts and Muslims. Egypt will emerge stronger and more united from this situation,” Egyptian president Abdel Fattah el-Sisi stated Dec. 11, as he declared a three-day period of national mourning.

The explosion occurred around 10 am local time during a Liturgy at the seat of the Coptic Orthodox Church. The Coptic Orthdox Church is an Oriental Orthodox Church, meaning it rejected the 451 Council of Chalcedon, and its followers were historically considered monophysites — those who believe Christ has only one nature — by Catholics and the Eastern Orthodox.

Egypt’s Christians, mostly Copts, make up 10 percent of Egypt’s 83 million-strong population, while the remaining 90 percent is Muslim. Christians in Egypt have long faced attacks from Islamist extremists, particularly since Egypt's military ousted president Mohammed Morsi, of the Muslim Brotherhood, in 2013.

In February, four Coptic teenagers were found guilty of insulting Islam and sentenced to five years imprisonment. And two persons were killed in clashes outside St. Mark's in April 2013. In Libya, the Islamic State killed 21 Coptic Orthodox from Egypt in February 2015. In 2011, a bombing on a Coptic church in Alexandria killed 23.

Following his Angelus address on Sunday, Pope Francis prayed for the victims of the attack, and stated that “there is only one answer” to such violence: “faith in God  and unity in human and civil values.” He also expressed his closeness to Tawadros II, the Coptic Orthodox Patriarch of Alexandria, “and to his community, praying for the dead and the wounded.”