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.
The explosive device was planted under a seat in the church, where it detonated in the main prayer hall.
"Terrorism hits Egypt again, this time on Palm Sunday. Another obnoxious but failed attempt against all Egyptians," the Foreign Affairs ministry tweeted.
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 attacked the church Sunday, 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.
"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.
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.
Pope Francis is scheduled to visit Cairo this month, where he will meet with various religious leaders, including the head of the Coptic Orthodox Church.
Tanta is roughly 60 miles (96 kilometers) north of Cairo, in the Nile delta.
There has been no immediate claim of responsibility.
The attack comes days after President Donald Trump welcomed Egyptian President Abdel Fattah al-Sisi to Washington and stressed his support for Cairo. Among the topics of mutual concern are terrorism and ISIS.