At least 21 people killed in explosion at Coptic Christian church in Tanta, Egypt, state media says

At least 21 people were killed by an explosion at a Coptic Christian church in northern Egypt during a service to celebrate Palm Sunday, state television reported. An additional 50 others were wounded in the blast at St. George (Mar Girgis) Coptic church in Tanta, it said. Palm Sunday is the Sunday before Easter, and marks the start of Holy Week for Christians. Social media video showed crowds gathered outside the church shortly after the attack. While it's unclear who the attackers were, Copts face persecution and discrimination that has spiked since the toppling of Hosni Mubarak's regime in 2011 . Dozens have been killed in sectarian clashes. In December, an attack at a Coptic church in Cairo killed 25 people. Read More "Coptic churches and homes have been set on fire, members of the Coptic minority have been physically attacked, and their property has been looted," rights group Amnesty International reported in March. CNN Map Coptic Christians make up about 10% of Egypt's population of 91 million. They base their theology on the teachings of the Apostle Mark, who introduced Christianity to Egypt. Tanta is roughly 60 miles (96 kilometers) north of Cairo, in the Nile delta.