A new Boko Haram video purports to show Islamic extremists repelling an advance by Nigerian troops in Borno state and beheading a captured soldier.

SITE Intelligence Group says the video distributed by the West Africa Province of the Islamic State group on social media Saturday "shows fighters clashing with enemy forces, dead bodies of slain soldiers, and the beheading of one soldier taken captive."

In a video Wednesday an unidentified man re-affirmed the group's allegiance to IS and its leader Abu Bakr al-Baghdadi. The man denied Nigerian military reports that 200 militants have surrendered.

The extremists have stepped up attacks in Nigeria and neighboring countries since President Muhammadu Buhari took office in May pledging to halt the 6-year-old uprising that Amnesty International says has killed 20,000 people.