(CNN) -- Egyptian authorities beefed up security Thursday as Coptic Christians warily ushered in Christmas Eve after a New Year's Day bombing in front of a church that killed nearly two dozen of their members.
The Coptic Christians celebrate Christmas according to the Julian calendar and therefore will observe it Friday.
"Police plan a large-scale security operation for tonight to protect Egypt's Coptic Christians and their churches." Col. Alla Mahmoud of the interior ministry said.
In addition, hundreds of supporters gathered outside the prestigious Al-Azhar University on Thursday in a show of solidarity for the Coptic community.
On Wednesday, Egyptian authorities released a sketch of a man they think may be responsible for the attack.
"The man in the picture is unknown and authorities are trying to confirm his identity," said Col. Alla Mahmoud of the interior ministry.
The interior ministry used forensic technology to recreate the face of the suspected suicide bomber responsible for killing 23 people when he detonated a car bomb outside The Church of the Two Saints in the city of Alexandria, the al-Ahram newspaper reported Wednesday.
The newspaper, which is majority-owned by the government, said the forensic experts estimate the suspected bomber was in his early 20s.
Citing officials, the newspaper also said that the bomber had packed about 20 to 25 kilograms (40-55 lbs) of explosives in a traveling bag, indicating that he may have been planning to enter the church or wait for congregants to come out when the explosives went off prematurely in the car.
About 9 percent of Egypt's 80 million residents are Coptic Christians, according to the CIA's World Fact Book.
The Coptic Church bases its theology on the teachings of the Apostle Mark, who introduced Christianity to Egypt, according to St. Takla Church in Alexandria, the capital of Coptic Christianity.
The religion is known for its rift with other Christians in the fifth century over the definition of the divinity of Jesus Christ.
Journalist Ian Lee contributed to this report from Cairo