ISIS is now claiming responsibility for the suicide bomb attack that killed 25 people in a Coptic cathedral in Cairo, Egypt.
The Islamic terrorist group warned of more attacks to come.
Egyptian authorities have identified the suicide bomber as Mahmoud Shafik Mohamed Mostafa, 22, but said he uses a different alias.
Authorities have made public a surveillance video which shows a figure who is said to be Mr. Mostafa as he entered the church, followed by a huge plume of dust and smoke from the blast a few moments later.
This is the deadliest terrorist attack to occur on Egyptian civilians in years and is the country's worst act of sectarian violence since the Coptic church bombing in Alexandria, Egypt in 2011.
The Islamic State also vowed to heighten its "war on polytheism," a reference to Christianity which is actually a monotheistic faith. The threat suggests that the group plans to intensify its operations in Egypt's biggest cities.
Coptic Christians make up about 10 percent of the Egyptian population and have complained for a long time about systematic discrimination against them.