Islamic State group claims deadly Cairo church bombing

The Islamic State group has claimed responsibility for the suicide bombing on Sunday which killed 25 people, mostly women and children, at a Coptic Christian church in Cairo.

According to a statement circulated by the militant group online, the bomber went by the nom de guerre Abu Abdullah al-Masry. The group vowed in the statement "to continue war against apostates".

Egyptian President Abdel Fattah al-Sisi named the bomber as 22-year-old Mahmoud Shafik Mohammed Mostafa, adding that four people were arrested in relation to the attack.

"This blow has caused us a lot of pain, but never will we let it break us," Sisi said.

The blast occurred at around 10am while worshippers were gathered for Sunday mass in a church adjacent to St. Mark's Cathedral, the seat of the Egyptian pope and the country's main church. 

The blast shattered windows and scattered pews through the interior of the church, scorching its marble pillars.

Security officials said they believed a bomb containing 12 kilos of TNT appeared to have been the cause of the explosion.

Sunday's attack was the deadliest act of violence committed against on the country's Coptic Christian community since a 2011 suicide bombing killed more than 20 worshippers outside a church in the coastal city of Alexandria.