The footage posted online late Thursday by IS-linked propaganda arm Amaq showed 11 blindfolded men being shot and stabbed by
"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.
IS leader Baghdadi committed suicide in October to avoid capture during a US special forces raid on his hideout in the province of Idlib in northwest Syria.
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
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
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.
ISWAP pledged allegiance to Baghdadi in 2016 and split from insurgent group Boko Haram.
It stepped up attacks on military outposts and troops in mid-2018, but has increasingly begun targeting civilians.
The violence had spread to