Coptic Christians are on high alert as they prepare this week for their Christmas holiday, following the deadly bombing at an Egyptian church on New Year's Day.
Egyptian authorities have increased security at Coptic churches ahead of the January 7 holiday when Copts celebrate Christmas. Officials say they have canceled police officers' leave and have tightened security at the country's ports and airports to prevent suspects from leaving Egypt.
Egyptian security officials have said local militants inspired by al-Qaida may have been responsible for the attack. They said they are investigating a group of radical Salafi Sunni Muslims based in Alexandria and have detained several people for questioning.
Meanwhile, authorities in France and Germany say they are investigating threats made by radical Islamists against Coptic Christians in their countries as well.
On Sunday, hundreds of Egypt's minority Christians held protests in the capital, Cairo, venting their anger at authorities for failing to protect them.
Protesters pelted a government minister's car and clashed with police outside Cairo's St. Mark's Cathedral. Protests also were held in the northern city of Alexandria, where an apparent suicide bombing at a Coptic church killed 21 worshippers and wounded scores of others on Saturday.
Pope Benedict on Sunday repeated his condemnation of the bombing, calling it an offense against "God and all of humanity."
No one has claimed responsibility for the attack. Egyptian President Hosni Mubarak has condemned the bombing, saying it was directed at "all Egyptians, not just Christians."
Mubarak said the bombing was the work of "foreign hands," and he vowed to defeat those plotting against Egypt's security.
Al-Qaida's affiliate in Iraq has claimed responsibility for recent bombings against Christians in Iraq and has made threats against Egyptian Christians. The group linked the violence to the case of two Egyptian women who it alleges are being held against their will by Christians for trying to convert to Islam.
Some information for this report was provided by AP, AFP and Reuters.