A policeman was killed while trying to dismantle an explosive device outside a Coptic church in Egypt on Saturday, a security source said.Two other officers were also wounded in the explosion as security personnel attempted to defuse the device in Nasr City on the edge of Cairo, the source added.It had been hidden inside a bag that was searched by police. The policeman who was killed, Mustafa Abid, was a specialist in mine clearance. Coptic Christians, who account for around 10 percent of Egypt's population, have been targeted in a string of attacks by the Islamic State group in recent years.The latest attack comes ahead of Christmas mass on Sunday when President Abdel Fattah al-Sisi is due to inaugurate the Cathedral of Nativity in Egypt's New Administrative Capital, 45 kilometres (28 miles) east of Cairo. Security has been reinforced in the capital in recent weeks ahead of Christmas, which Egypt's minority Coptic Christians will celebrate on January 7. The country's leader since 2014, Sisi often presents himself as a defender of Christians against extremists. * Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook. But activists and some analysts accuse the state of discriminating against them and not providing enough protection.More than 100 Copts have been killed in jihadist attacks since December 2016.IS claimed an assault in early November which killed six Copts and one Anglican in the central province of Minya. The police later said 19 suspected jihadists linked to the attack had been killed in a shootout.IS also killed more than 40 people in twin church bombings in April 2017, and an IS gunman in December that year killed nine people in an attack on a church in a south Cairo suburb.Hundreds of police and soldiers have also been killed in attacks, and last week three Vietnamese tourists and their Egyptian guide died when a homemade bomb exploded on their bus on the outskirts of Cairo. The country has been under a state of emergency since April 2017.