Cairo church bombing kills 25, raises fears among Christians

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The attack comes as President Abdel Fattah al-Sisi fights battles on several fronts. His economic reforms have angered the poor, a bloody crackdown on the Muslim Brotherhood has seen thousands jailed, whilst an insurgency rages 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.

Egyptian security officials and investigators inspect the scene following a bombing inside Cairo's Coptic cathedral in Egypt December 11, 2016. REUTERS/Amr Abdallah Dalsh

There was no immediate claim of responsibility, but exiled Brotherhood officials and home-grown militant groups condemned the attack. Islamic State supporters celebrated on social media.

"God bless the person who did this blessed act," wrote one supporter on Telegram.

The explosion took place in a chapel, which adjoins St Mark's, Cairo's main cathedral and the seat of Coptic Pope Tawadros II, where security is normally tight.

The United States said it "will continue to work with its partners to defeat such terrorist acts" and that it was committed to Egypt's security, according to a White House statement on Sunday.

The UN Security Council urged "all States, in accordance with their obligations under international law and relevant Security Council resolutions, to cooperate actively with all relevant authorities" to hold those responsible accountable.

At the Vatican, Pope Francis condemned what he called the latest in a series of "brutal terrorist attacks" and said he was praying for the dead and wounded.

The chapel's floor was covered in debris from shattered windows, its wooden pews blasted apart, its pillars blackened. Here and there lay abandoned shoes and sticky patches of blood.

"As soon as the priest called us to prepare for prayer, the explosion happened," Emad Shoukry, who was inside when the blast took place, said.