The Islamic State group has released a video claiming to show the killing of 11 Christians in Nigeria. ISIS said it was part of its recently declared campaign to “avenge” the October deaths of its leader and spokesman in Syria.

On Friday, Buhari condemned the purported killers as “remorseless, godless, callous gangs of mass murderers that have given Islam a bad name through their atrocities”.

He also called for unity among Nigeria’s Christians and Muslims. “These agents of darkness are enemies of our common humanity, and they don’t spare any victim, whether they are Muslims or Christians.”

In recent months, Islamic State in West Africa Province (ISWAP) has intensified its attacks on Christians, security personnel and aid workers, setting up roadblocks on main roads and conducting searches.