Egypt's Coptic Pope Shenouda III appealed for calm on Monday as Christian protesters clashed with police for a third day in a row after a New Year's Day bombing killed 21 churchgoers and wounded scores others.
The spiritual head of the Middle East's largest Christian minority also called on the government to address his flock's grievances.
The unrest came as police went on high alert and tightened church security for Christmas, which Copts celebrate on Friday, as investigators hunted the perpetrators of the Alexandria church bombing.
Tensions spilled over again late on Monday as protesters in a northern Cairo neighborhood threw rocks at police who tried to block a march by thousands of Copts.
Riot police responded by throwing rocks back at the protesters, who also pelted armored police cars with stones and bottles.
An AFP correspondent said at least 10 protesters were wounded, several of them carried away bloodied by stones hurled from police lines.
The official MENA news agency reported that two officers and 12 policemen were wounded in the clash.
"I call on our sons for calm, as calm can solve all issues," the Coptic leader said in an interview with the state TV, the text of which was also published by the MENA.
"The slogans used by some have transgressed all values and manners... and some have tried to use violence, while violence is absolutely not our method," he said, blaming unspecified people he said were unrelated to his community.
Protesters also blocked a ring-road in two districts of the Nile Delta province of Qalubiya, burning tyres and stoning cars, MENA reported.
Monday's unrest came a day after 45 policemen were wounded in a confrontation with Coptic protesters outside St. Mark's Cathedral in Cairo, where the Coptic pope has his headquarters.
Protesters also threw rocks at a minister who had come to visit the pope, and a health ministry official said 27 other people were wounded in the clash.
Copts, who make up about 10 percent of Egypt's 80 million people, have been targets of sectarian attacks and complain of discrimination, such as the legal requirement for them to obtain presidential permission to build churches.
In the interview, Shenouda said the state must address Coptic complaints.
"If it finds a law that harms some, the state has to correct the law or legislate new ones," he said.
Coptic Christmas this year falls on Friday, the weekly Muslim day of prayer and rest, and Shenouda said he intended to say mass as usual on Christmas Eve.
Egyptian security forces cancelled leave for senior officers and tightened surveillance of airports and ports to prevent suspects from leaving the country, as new checkpoints were set up across the nation.
"Security is preparing a list of those who have arrived in Egypt recently from countries where al Qaeda is known to recruit operatives," a security source said.
Saturday's attack also wounded 79 people when an apparent suicide car bomber detonated his payload as hundreds of worshippers were leaving al-Qiddissain (The Two Saints) church in Alexandria after midnight.
It immediately sparked protests by angry Copts who called for protection and justice.
Another security official said on Sunday that about 20 people were detained for questioning, but there was no evidence that any of them was directly connected to the attack in the northern Egyptian city.
Egyptian officials have said there were indications "foreign elements" were behind the blast and said the attack seemed to have been the work of a suicide bomber.
"The security forces have confirmed that finger of suspicion indicates that the culprit was a suicide bomber linked to al-Qaeda," a security source, who asked not to be identified, said.
No one has yet claimed responsibility for the attack, which came two months after an al-Qaeda-linked group said it was behind a deadly Baghdad church hostage-taking and threatened Coptic Christians as well.
The group demanded the release of two women, both priests' wives, saying the Coptic church was holding them against their will after they converted to Islam. The church denies they have converted.
Two weeks ago, a statement on an al-Qaeda-linked website urged Muslims to attack Coptic churches in Egypt and among Egyptian Christian communities in Germany, France, Britain and elsewhere around Christmas, which Orthodox Copts celebrate on Jan. 7.
The website that published that threat posted in December a list of Coptic churches in Egypt and Europe it said should be attacked, including al-Qiddissain church in Alexandria.
Copts in Europe
Copts, the native Christians of Egypt, are the biggest Christian community in the Middle East and also have diaspora communities in the United States and Europe. They worship in a nearly-extinct language descended from ancient Egyptian.
In Europe, authorities said they were pursuing threats against Coptic churches there, after militants said they would attack the Egyptian Christian denomination both in Egypt and among its diaspora communities.
A French security official said on Monday that police were investigating threats against Coptic churches and would reinforce security at 19 of the churches.
The German government said it had warned Coptic Christians living in Germany about the risk of possible attacks just hours before the New Year's blast in Alexandria.
"I can confirm that on New Year's Eve the interior ministry contacted the bishop of the Coptic Christians in Germany, Anba Damian, to tell him about this risk," German Interior Ministry spokesman Stephan Paris told reporters.
The Austrian interior ministry said it would secure the country's seven Coptic churches.
The Alexandria bombing has further underscored the vulnerability of the Copts.
Last year began with a massacre of six Copts and a Muslim security guard after a Coptic Christmas Eve mass and ended with two Coptic protesters killed in clashes during a protest over a Cairo church permit.