Nine people died when gunmen tried to storm a church south of Cairo, but were intercepted by police, officials say.
Three of the dead were police who were on duty at Mar Mina church.
One attacker was killed and his explosives belt was defused. Another gunman managed to escape.
Security services announced plans this week to protect festivities around the New Year and Coptic Christmas.They include the deployment of rapid reaction forces and jamming equipment.
Friday's attack appears to have taken place when police patrolling the church noticed two men behaving suspiciously, reports the BBC's Radwa Gamal in Cairo.
They approached the men, who began firing. There are reports that several people were wounded, two critically.
According to our correspondent, the explosives belt discovered on the dead assailant suggested an even more deadly attack was planned.
Egypt's Copts have in the past accused authorities of only token gestures to protect them and this incident will not help calm tensions, she says.
Egypt is a Muslim-majority country and its Christian minority - mostly members of the Coptic Orthodox Church - make up around 10% of the population.
Last April at least 45 people died in twin attacks on Coptic churches in Alexandria and the Nile Delta city of Tanta. At least 29 Copts were killed on a bus in May and a Coptic Orthodox priest was stabbed to death in Cairo in October.
The attacks have been blamed on, and in some cases claimed by, Islamists affiliated with so-called Islamic State (IS).