A policeman has been killed trying to defuse a bomb outside a church in Egypt, security officials said.

The explosion injured two other officers and an onlooker. The device was hidden in a bag on a roof by the Coptic Christian church in Nasr City outside Cairo, the BBC reported on Sunday.

It comes two days before Egypt’s Christians celebrate their Christmas.

About 10 per cent of Egypt’s population is Copts and many accuse the state of discriminating against them and not offering them enough protection.

No group has claimed the attack yet but Islamist insurgents have regularly attacked Copts in the past.