At least 25 people were killed and dozens more injured when a bomb went off inside a Christian church in Cairo on Sunday.

In a report published on CNN, Egyptian authorities reveal that the bomb was a 12-kilogram TNT explosive that rocked the St. Peter and St. Paul Church annexed to St. Mark's Coptic Orthodox Cathedral located in the Abbaysia district.

The bomb blasted around 10 AM during the middle of a Sunday worship service. Most of the victims were women and children. This has been the deadliest bombing of a place of worship in recent history in Cairo.

President Abdel Fattah El-Sisi immediately issued a statement condemning the attack and declared a three-day national mourning and prayers for peace. The highest religious law official - the Grand Mufti - also deplored the attack.

No group has so far claimed responsibility for the attack. This recent attack came after two bombs blasted Saturday that killed six policemen and another civilian along the Giza Haram district that leads to the city's historic pyramids.

"Attacking churches whether by demolition, bombing, killing those inside, or terrifying ... secure people are prohibited in Islamic Sharia," religious leader Sheikh Shawky Ibrahim Abdel-Karim Allam said. He also sent condolences to the Coptic Church leadership in Alexandria.

Coptic Christians comprise around 10 percent of the 91 million population in Egypt, whose religious history follows the teachings of Mark the Apostle who was responsible for bringing Christianity to Egypt. Alexandria is the Coptic Christianity capital in the region. The Copts belong to the earliest groups of Christian believers outside of the Holy Land.

The persecution of Coptic Christians can be traced back to the ouster of former president Hosni Mubarak back in 2011, for which dozens have been killed in what could have been claimed as religious sectarian clashes.

One of the most popular incidents was the ISIS abduction of almost a dozen Coptic Christians who were then marched off to the beach only to be beheaded in front of a video camera and uploaded online for the world to see.

Over the years, the Coptic Christians in Egypt have also been at the receiving end of complaints after the Egyptian court found three believers guilty with a sentence of three to five years. The children were allegedly insulting Islam when they were collared. The suspects claimed they their actions were focused on the instead, on attacking Islam under ISIS.