A bombing at Cairo's largest Coptic cathedral has killed at least 25 people and wounded 49, many of them women and children attending Sunday mass, in the deadliest attack on Egypt's Christian minority in years.
The attack comes as Egyptian President Abdel Fattah al-Sisi battles against an Islamist insurgency in Northern Sinai, led by the Egyptian branch of Islamic State.
The militant group has also carried out deadly attacks in Cairo and has urged its supporters to launch attacks around the world in recent weeks as it goes on the defensive in its Iraqi and Syrian strongholds.
There was no immediate claim of responsibility, but Islamic State supporters celebrated the attack on social media.
"God bless the person who did this blessed act," wrote one supporter of the militant group on Telegram.
The explosion took place in a chapel adjoining the main hall of St Mark's Cathedral, the largest in the metropolis of 20 million, where security is normally tight.
"As soon as the priest called us to prepare for prayer, the explosion happened," Emad Shoukry, who was inside when the blast took place, told Reuters.
"The explosion shook the place... The dust covered the hall and I was looking for the door, although I couldn't see anything... I managed to leave in the middle of screams and there were a lot of people thrown on the ground."
Security sources told Reuters at least six children were among the dead, with the blast detonating on the side of the church normally used by women.
They said the explosion was caused by a device containing at least 12kg of TNT. Police were investigating claims by witnesses that the bomb was concealed in the handbag of a woman who had placed it on the floor of the church and left.
Police and armoured vehicles rushed to the area, as dozens of protesters gathered outside the compound demanding revenge. Scuffles broke out with police.
Though Egypt's Coptic Christians have traditionally been supporters of the government, angry crowds turned their ire against Sisi, saying his government had failed to protect them.
"As long as Egyptian blood is cheap, down, down with any president..." they chanted.
Sisi's office condemned the attack as an act of terrorism and declared three days of national mourning. Al Azhar, Egypt's main Islamic centre of learning, also denounced the attacks.
Orthodox Copts, who comprise about 10 percent of Egypt's 90 million people, are the Middle East's biggest Christian community.
Egypt's Christian community has felt increasingly insecure since Islamic State spread through Iraq and Syria in 2014, ruthlessly targeting religious minorities. In 2015, 21 Egyptian Christians working in Libya were killed by Islamic State.
Coptic Pope Tawadros II cut short a visit to Greece after learning of the attack.