One of two known blasts struck at a Coptic Church in the Nile Delta City of Tanta, 75 miles north of Cairo. The other in Alexandria killed 16+. Some sources claim at least 45 were killed as a total for both attacks.
Palm Sunday is one of the holiest days of the Christian calendar, marking the triumphant entrance of Jesus to Jerusalem. It is celebrated by the Coptic Church, as well as in the West.
The state-run Nile television channel said the explosion struck inside the Mar Girgis Coptic Church in Tanta just before 10:00am (0800 GMT).
"Either a bomb was planted or someone blew himself up," provincial governor Ahmad Deif said, adding that security forces had searched the church and surrounding areas for additional explosive devices.
The atrocity, which followed another attack in Tanta, was thought to have been aimed at Pope Tawadros II, leader of the ancient Coptic church, who was worshipping in St Mark's at the time but escaped unharmed.
Now, it appears obvious, after the USA attack against Syria, American church bodies and other gatherings will be on high alert for potential Easter Sunday terrorist attacks.