The Suicide bomber, nicknamed Abu Abdullah al-Masry, blew himself up with an explosive belt, the terror group said in a statement circulated online.
Egypt President Abdel Fattah el-Sisi, while attending the State funeral of the victims on Monday, said a 22-year-old suicide bomber called Mahmoud Shafik Mohamed Mostafa was behind the attack.
He said that four persons including a woman were arrested.
Twenty-five worshippers, mostly women and children, were killed and nearly 50 injured when the powerful blast ripped through the church adjacent to Egypt's main Coptic Christian cathedral here during a Sunday mass, the deadliest attack against the minority community in recent times.