The footage posted in an online Telegram news channel late on Thursday by ISIL-linked propaganda arm Amaq showed 11 blindfolded men being lined up at an unidentified outdoor location.
One man is shot before the other 10 are beheaded. A masked man in the almost one-minute video claimed the killings were in response to the death of ISIL chief Abu Bakr al-Baghdadi and his spokesman.
‘Remorseless, godless, callous’
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.
A previous video, seen by Reuters News Agency, said the captives had been taken from Maiduguri and Damaturu in Nigeria’s northeast, where fighters have been attempting for years to set up a separate state under Islamic law.
In that earlier video, the captives pleaded for the Christian Association of Nigeria and President Muhammadu Buhari to intervene and save them.
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.”
ISWAP split from Nigerian armed group Boko Haram in 2016, pledging allegiance to al-Baghdadi.
It stepped up attacks on military outposts and troops in mid-2018 but has increasingly begun targeting civilians.
The decade-long armed uprising in northeast Nigeria has killed 36,000 people and displaced around two million, according to the United Nations.