Egypt has tightened security as Coptic Christians mark their traditional Christmas, following a New Year's Day suicide church bombing that killed 23 worshipers in Alexandria.
Copts are gathering in large numbers Thursday for Christmas Eve services.
Authorities say police have set up a large-scale security operation to protect the worshipers.
In Vatican City, Pope Benedict XVI sent ‘heartfelt greetings’ to Christians in Eastern churches who are celebrating Christmas on Friday, under the Coptic calendar.
In an apparent reference to the Egypt blast, the pontiff said he was praying that God would strengthen and comfort communities that are suffering.
Also Thursday, Egyptian police released a sketch of the suspected suicide bomber. Authorities say they created the image based on evidence found at the scene, including parts of the alleged bomber's head.
No one has claimed responsibility for the blast, but authorities suspect al-Qaida.
The church bombing sparked riots and complaints of discrimination against Christians.
Last year, on Coptic Christmas Eve, gunmen killed six Coptic worshippers as they were leaving services in Cairo.