An Egyptian policeman was killed early Sunday morning and four others were injured when a roadside bomb exploded outside Cairo, Reuters reported.

The Egyptian Interior Ministry said that “as a vehicle belonging to the Central Security Forces transported a group of officers and conscripts an improvised explosive device planted on the roadside went off.”

Authorities were investigating the blast and questioning residents in the area.

Egypt has in recent years been battling a stepped-up insurgency in northern Sinai, mainly by militants from an Islamic State group affiliate.

The militant campaign accelerated after the military ouster of elected Islamist president Mohammed Morsi in 2013.

The Islamic State affiliate in Sinai has often attacked police and soldiers, but has also claimed several deadly attacks on civilians, including over 100 Coptic Christians in attacks on churches and convoys since December 2016.

The group also claimed responsibility for the downing of a Russian passenger plane over the Sinai in 2015, which killed all 224 people on board and devastated Egypt’s tourism industry.