Ceremonial tents are being set up outside some Coptic churches for the celebrations
Coptic Christians are preparing to celebrate Christmas Eve amid tight security after a bomb attack on a church in Egypt in which 21 died.
There have been calls for Muslims to hold vigils outside Coptic churches in a gesture of solidarity.
But some radical Islamist websites have urged more attacks, publishing church addresses in Egypt and Europe.
The bombing of the church in Alexandria on New Year's Day was the worst act of sectarian violence in Egypt in a decade.
It triggered days of protests and riots by Christians blaming the government for encouraging discrimination and not doing enough to protect them.
In response, Egyptian authorities have stepped up security around many churches, with explosives experts on hand.
Armoured vehicles have also been stationed in key areas.
Egyptian activists have called for Muslims to form human shields around churches during Thursday's Christmas Eve celebrations as a gesture of solidarity with Christians.
However, radical Islamist websites have been circulating lists of Coptic churches in Egypt and Europe with instructions on how to attack them.
"Blow up the churches while they are celebrating Christmas or any other time when the churches are packed," the statement read.
Copts celebrate Christmas on 7 January, according to the Julian calendar. Some European governments have also announced security measures at churches.
The BBC's Jon Leyne in Cairo says suspicion and fear between Christians and Muslims has been growing in Egypt for some time, made worse by tough economic conditions and a discredited political system.
It was during Coptic Christmas Eve celebrations in southern Egypt in 2009 that six Christians and a Muslim security guard were killed in a drive-by shooting.
The country's Coptic Christian minority makes up 10% of Egypt's 80 million people.
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