Islamic State’s West Africa branch claimed responsibility for a raid in Nigeria in which it said 20 soldiers were killed and released a video apparently showing the execution of nine Nigerian soldiers.
A security source and a humanitarian worker, both requesting anonymity, said insurgents struck the north-eastern town Gubio in Borno state on Monday in vehicles mounted with heavy machine guns and on motorbikes.
Insurgents and soldiers exchanged fire for more than an hour before the army withdrew, said the humanitarian worker, who counted the corpses of more than 15 soldiers.
A Nigerian military spokesman said he would send a comment on the Islamic State claim, but at the time of writing had not.
Nigeria said the insurgency and its rival Boko Haram are on the back foot as the sides engage in a battle of propaganda to show who has the upper hand in the decade-long conflict.
The war killed more than 30,000 and displaced millions more.
The Islamic State branch said in its claim of responsibility, translated into English and published by SITE Intelligence, its fighters attacked an army barracks and killed 20 soldiers in Gubio on Monday.
In a separate video, Islamic State West Africa showed the execution of nine Nigerian soldiers. It was not immediately possible to independently verify the video.
Before their executions, the soldiers identified themselves by their military service numbers, units and names. Some said where and when they were captured.
The video showed Islamic State fighters pledging allegiance to leader Abu Bakr al-Baghdadi, along with artillery, tanks and boats it said were captured from the military and attacks on Nigerian bases.
Islamic State West Africa has made claims of responsibility for attacks over past months, some verified by security sources and others with knowledge of their attacks.