Egypt said Monday it had arrested four people suspected of involvement in a devastating bombing of a Cairo Coptic church, as grief-stricken mourners gathered for the funeral of the dead.
The health ministry said 25 people had been killed in the bombing at the Saint Peter and Saint Paul Church on Sunday.
It was the deadliest attack in recent memory on the Christian minority, who make up about 10 percent of Egypt's population.
President Abdel Fattah al-Sisi, speaking at the funeral, said the attack was carried out by a suicide bomber who had been identified as 22-year-old Mahmoud Shafik Mohamed Mostafa.
One of the four people arrested was a woman, Sisi said, and authorities were looking for two other suspects he did not identify.
Most of the victims were women, authorities have said.
The attack occurred during Sunday service at the church adjacent to Saint Mark's Cathedral, the seat of Coptic Pope Tawadros II.
There has been no claim of responsibility for the bombing, but Coptic Christians have been previously targeted in Egypt.
Wooden coffins, each bearing a cross, were covered with the country's flag and lined up at the Saint Mary and Saint Athanasius Coptic Orthodox Church in the Nasr City district on Monday.
A woman who lost two daughters in the attack cried and fell to the ground next to their coffins as other mourners prayed silently.
- Sisi leads mourning -
In the streets of Nasr City, Sisi and Tawadros led black-clad mourners behind soldiers carrying the coffins of the victims.
Troops marched to the sound of military music.
"This blow has caused us a lot of pain, but never will we let it break us," Sisi said.
Pope Tawadros II said: "We are hurting from this evil."
Sunday's blast was the worst attack on the Coptic Christian community since a 2011 suicide bombing killed more than 20 worshippers outside a church in the coastal city of Alexandria.
The health ministry said in a statement late Monday the death toll had risen to 25 after a 40-year-old woman died of extensive injuries.
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Copts have faced persecution and discrimination dating back to the 30-year rule of Hosni Mubarak, who was toppled by a popular uprising in 2011.
After the 2013 ouster of Muslim Brotherhood president Mohamed Morsi, his Islamist supporters accused the Christian community of supporting his overthrow.
They pointed to the appearance of Tawadros next to Sisi in July 2013, when the then army chief -- also surrounded by Muslim and opposition figures -- announced Morsi's removal on television.
Following the deadly dispersal by security forces of two pro-Morsi protest camps in Cairo in August 2013, at least 42 churches were attacked, as well as dozens of schools, houses and businesses belonging to Copts, according to Human Rights Watch.
"Egypt's authorities have for many years failed to protect the personal safety or basic rights of Coptic citizens," HRW said on Monday.
- 'Slap for the government' -
Analysts said Sunday's bombing revealed the weaknesses of the government, which human rights groups have slammed for its brutal crackdown on Islamists.
Victor Salama, a politics professor at Cairo University, said the attack could be in retaliation for the church's perceived support for Sisi's administration.
The Islamists "could be saying they're making the Copts pay for their support for the ouster of the Muslim Brotherhood," said Salama.
"It's a slap for the government. The Coptic church is Christian of course, but it's also an Egyptian institution that was easily destroyed with just 12 kilogrammes of explosives," said Salama.
Abdalla al-Sennawi, a columnist at the privately owned Al-Shorouk newspaper, agreed that the attack could be seen as "a sort of revenge" against the Copts.
But the bombing also "reveals the absence of any real strategy to fight terrorism and the carelessness of the security services", he said.
"Such attacks may repeat themselves if the role of security services is not reviewed."
Egypt is fighting a jihadist insurgency that has killed hundreds of policemen and soldiers.
On Friday, two bombings killed six policemen in Cairo and a civilian north of the capital in attacks claimed by the Hassam militant group.
Hazem Hosni, a politics professor at Cairo university, said: "The objective of this attack will be truly known only if the perpetrators of the attack are identified or if they claim it."
Sunday's bombing "will have great international impact because those targeted are Christians", he said.
Egypt has jailed thousands and sentenced hundreds of Islamists to death since Morsi's ouster.