|Scenes of grief and anger marked the Sunday Mass al-Qiddissine church, struck by a car bomb the previous day [AFP]
Angry Coptic Christians have clashed with police as they demanded more protection for Egypt's Christians following a New Year's Day church bombing that killed 21 of their brethren.
Hundreds of members of Egypt's large Christian minority protested in Cairo and Alexandria, the northern city where the presumed suicide bomber detonated a device outside a church during a midnight service.
At Saint Mark's Cathedral, the Cairo base of Orthodox Pope Shenouda, several hundred young Copts fought police on Sunday as they tried to leave the cathedral grounds and take to the streets to demand more protection for Christians.
Their protest continued into the night, the crowd held back by a cordon of riot police nine men deep. A church official approached the crowd briefly to try to calm them down, without success.
Egypt is holding seven people for questioning over the New Year's Day bombing.
Sunday's announcement came as congregants were back praying in al-Qiddissine [The Saints] church, targeted the day before by a car bomb that also wounded 97 people.
Reuters news agency, citing security sources, reported later that 10 of the 17 originally held were released, with the remaining seven being detained for questioning.
Earlier, protestors in Cairo had heckled government officials who visited the cathedral compound to offer condolences.
Some protesters pelted a minister's car with stones when he left, witnesses said. Some visiting Christian officials had cars shaken by angry demonstrators, while other protesters scuffled with police outside the compound.
Extra police officers were posted outside several churches in Cairo and Alexandria on Sunday, preventing cars from parking next to the buildings, witnesses said
Dozens of worshippers attended Sunday Mass at the church, located in the Sidi Bechr district of the Mediterranean port city of Alexandria, while riot police backed by armoured vehicles were deployed outside.
The service was marked by the grief and anger felt by a congregation devastated by the attack, which took place on Saturday outside the church's door about 30 minutes into the New Year.
Many wept while others cried hysterically, screamed in anger or slapped themselves.
"We spend every feast in grief," Sohair Fawzy, who lost two sisters and a niece in the attack, said.
Grim reminders of the attack remained in the church a day after the bombing. Its ground floor was stained with the blood of victims brought inside immediately after the attack.
Two statues of Christ and the Virgin Mary were toppled and the benches were scattered by the impact of the blast. A "2011" sign hung on the inside of the church's door was torn apart.
The attack was the worst violence against Egypt's Christian minority in a decade.
It sparked clashes between riot police and Christians who say the government hasn't done enough to protect them.
The Copts are the biggest Christian community in the Middle East and account for up to 10 per cent of Egypt's 80 million population.
No bombing claim
There was no immediate claim of responsibility for the bombing, which came as nearly 1,000 faithful left al-Qiddissine church.
According to the Egyptian interior ministry, the car that exploded was parked in front of the church.
After the blast, enraged Christians emerging from the church fought with police and stormed a nearby mosque.
Al Jazeera's Ayman Mohyeldin, reporting from the Egyptian capital Cairo, said that the car bomb probably involved sophisticated remote-control timer technology.
"Churches in Egypt are heavily guarded, so undoubtedly questions will arise about how a car was parked so close to the church and who was able to detonate it from a distance," he said.
While it was not known who was responsible for the blast, a group calling itself "al-Qaeda in Iraq" had threatened the country's Coptic Christian community.
Egyptian police said on Sunday they are focusing their investigation on an Alexandria-based group inspired by al-Qaeda, but not under foreign command.
Security officials said that they were also examining lists of air passengers who arrived in Egypt recently from Iraq, in response to the threats from the Al-Qaeda in Iraq group.
They said they were looking for any evidence of an al-Qaeda financier or organiser who may have visited Egypt to recruit the bomber and his support team from the local population.
Investigators were also examining two heads found at the site of the attack, on the suspicion that one of them belonged to the bomber, state news agency MENA reported.
The crime lab investigation found the explosives used were locally made and were filled with nails and ball bearings to maximise the number of casualties.
The attack in Egypt prompted Pope Benedict XVI in the Vatican to call for Christians to remain strong in the face of intolerance and violence in a New Year's appeal on Sunday.
It echoed comments last month in which he called a lack of religious freedom a threat to world security.
"In the light of this strategy of violence which is targeting Christians but has consequences on the whole population, I pray for the victims and for their families and I encourage the ecclesiastic communities to persevere in faith and in the testimony of non-violence which comes from the Gospels," he said.
The bombing comes almost two months to the day after an October 31 attack by fighters on Our Lady of Salvation church in central Baghdad, which left 44 worshippers, two priests and seven security forces members dead.
Al-Qaeda's Iraqi affiliate claimed responsibility for that attack and made new threats against Christians.
The group threatened to attack Egyptian Copts if their church did not free two Christians it said had been "imprisoned in their monasteries" for having converted to Islam.
The two women were Camilia Chehata and Wafa Constantine, the wives of Coptic priests whose claimed conversion caused a stir in Egypt.
Protection around Copt places of worship was discreetly stepped up after the threats, as Hosni Mubarak, the Egyptian president, said he was committed to protecting the Christians "faced with the forces of terrorism and extremism".
Source: Al Jazeera and agencies