The Egyptian authorities have increased security at churches nationwide ahead of 7 January, when Coptic Orthodox Christians celebrate Christmas.
Security is typically tight at churches on major holidays. On New Year’s Day in 2011, a deadly bombing at a church in Alexandria killed 23 people.
On Tuesday, unknown gunmen shot and killed two Egyptian policemen guarding a Catholic church in the southern Egyptian city of Minya.
The Catholic church has reportedly cancelled planned celebrations to mark 7 January, in a spirit of mourning.
Osama Metwaly, head of Minya's security directorate, said a "terrorist group" was behind the attack, aiming to stir chaos in the country and to retaliate against the police.
Militant attacks on security forces have become common since the ouster of president Mohamed Morsi in 2013, with dozens of security personnel killed by bombings, shootings and other attacks.
Churches and Christian properties have also come under attack by extremists, most notably on 14 August 2013 when a wave of violence following the violent dispersal of two pro-Morsi protest camps saw dozens of churches razed to the ground.
Pope Tawadros II, the head of the Coptic Orthodox Church, is to lead the annual sermon at Cairo’s Abbasiya cathedral late on Tuesday, with the attendance of a number of state officials as well as thousands of worshippers.
Coptic Orthodox Christians, who make up around 90 percent of Egypt’s Christians, break their 43-day fast and celebrate Christmas on 7 January, almost two weeks after most Western denominations. The difference results from the use of different calendars.
The Patriarch of the Ethiopian Orthodox Tewahedo Church, Mathias I, will visit Egypt for the first time on Saturday, three days after Christmas.
The Egyptian and Ethiopian churches are seen to have played a role in the negotiations between both countries regarding the Grand Renaissance Dam Ethiopia is building on the Blue Nile, which Cairo is concerned could have an adverse effect on Egypt's water supply.