Jihadists aligned to the Islamic State group have released a video claiming to show the execution of 11 Christians in restive northeast Nigeria.
The footage posted online late Thursday by IS-linked propaganda arm Amaq showed 11 blindfolded men being shot and stabbed by jihadists from the Islamic State West African Province (ISWAP) at an undisclosed location.
"This is a message to Christians all over the world," said a masked man in the one-minute video.
He claimed the killings were in reprisal for the death of IS chief Abu Bakr al-Baghdadi and his spokesman.
In recent months, ISWAP has intensified its attacks on Christians, security personnel and aid staff, setting up roadblocks on highways and conducting searches.
The United Nations on Tuesday condemned the "increasing practice by armed groups to set up checkpoints targeting civilians" in the northeast of Nigeria.
On Sunday, the jihadists killed six people and abducted five others including two aid workers when they intercepted vehicles on a highway on the outskirts of Maiduguri, the Borno state capital.
In a similar attack on December 5, ISWAP fighters disguised as Nigerian soldiers stopped and searched vehicles at a checkpoint near Maiduguri.
The group claimed in a statement that six soldiers and eight civilians, including two Red Cross workers, were among those abducted in that attack.
Last week the group released a video showing 11 alleged hostages.
One of the detainees in the video who identified himself as a school teacher said all the 11 hostages were Christians and appealed to the Nigerian government to secure their release.
Nigeria's President Muhammadu Buhari said Friday he was "saddened and shocked by the death of innocent hostages in the hands of remorseless, godless, callous gangs of mass murderers".
"We should, under no circumstance, let the terrorists divide us by turning Christians against Muslims because these barbaric killers don't represent Islam," he said in a statement.
Buhari pledged to "continue to intensify our efforts towards strengthening international cooperation and collaboration to break the backbone of these evil doers".
The decade-long jihadist insurgency in northeast Nigeria has killed over 36,000 people and displaced around two million, according to the United Nations.
The violence has spread to neighbouring Niger, Chad and Cameroon, prompting a regional military coalition to fight the militants.
ISWAP pledged allegiance to Baghdadi in 2016 and split from the main insurgent group Boko Haram.
It stepped up attacks on military outposts and troops in mid-2018, but has increasingly begun targeting civilians.
The Nigerian government has repeatedly said that the insurgency is defeated but the jihadists maintain the ability to strike across swathes of territory.