An Islamist terrorist faction says it has executed 11 Christian aid workers in Nigeria.
The claim was made by the Islamic State in West Africa Province in a 56-second video published through Amaq, the IS propaganda media wing.
The Washington-based SITE Intelligence Group says that the footage shows one man being shot dead, with the others - all male - being beheaded by jihadists wearing black masks and beige uniforms.
The hostages were slain the day after Christmas, with terrorism analysts telling the BBC that the timing appeared to be strategic.
According to SITE, a voiceover to the video says that the deaths are in retaliation for the killings of IS leader Bakr al-Baghdadi and his spokesman in two separate US military operations earlier this year.
"This message is to the Christians in the world," the voiceover says.
"Those who you see in front of us are Christians, and we will shed their blood as revenge for the two dignified sheikhs, the caliph of the Muslims, and the spokesman for the Islamic State, Sheikh Abu al-Hassan al-Muhajir, may Allah accept them."
Reuters reports that another video released by the group suggests that the men were taken hostage in Maiduguri and Damaturu, in Borno, northeastern Nigeria, where militants have been attempting to create a separate Islamist state.
Reuters reports that the captives pleaded in the video for the Christian Association of Nigeria and President Muhammadu Buhari to save them.
President Buhari called the killings "barbaric".
"We should, under no circumstance, let the terrorists divide us by turning Christians against Muslims because these barbaric killers don't represent Islam and millions of other law-abiding Muslims around the world," he said.
In a message on Twitter Friday, Buhari added, "These agents of darkness are enemies of our common humanity and they don't spare any victim, whether they are Muslims or Christians, and therefore, we shouldn't let them divide us and turn us against one another."