A video released by Boko Haram purporting to show two beheadings shows that it is "incorporating itself into the Islamic State", an organisation that monitors terrorist groups has warned.

Veryan Khan, editorial director of the Terrorism Research & Analysis Consortium [TRAC], told Fox News that the latest release "shows Boko Haram is not a mere copycat of ISIS; rather, it is incorporating itself into the Islamic State."

ISIS supporters are "already starting to call Boko Haram the 'Islamic State Africa," Khan said.

Entitled 'Harvest of Spies', the six-minute video was posted on Twitter on March 2. Two men are shown kneeling with their hands tied behind their backs, while a militant dressed all in black stands over them with a knife. One of the men confesses to having spied on Boko Haram, and the film then cuts to a scene showing their two decapitated bodies.

The footage bears similarity to videos released by Islamic State, raising concerns that it is trying to emulate the Middle Eastern terrorist group. The leader of Boko Haram, Abubakar Shekau, last year declared his militants to have begun an Islamic caliphate in northern Nigeria, where it has been increasing its control in recent months.

"Thanks be to Allah who gave victory to our brethren in Gwoza and made it part of the Islamic caliphate" he said in a video after the capture of the town in Borno state on August 6.

Dr Khataza Gondwe, team leader for Africa and the Middle East at Christian Solidarity Worldwide, has previously warned of "coercion and cooperation" between jihadi groups such as Islamic State and Boko Haram operating in different countries.

"Boko Haram has always asserted its links to the international jihadist movement, and has said it received training from Somalia and Al Qaeda in the Islamic Maghreb (AQIM). There have always been links [with other jihadi groups]," Gondwe told Christian Today.

"Shekau acclaimed the Caliphate [Islamic State], and each group seems to be emulating or adopting tactics of the other."

Boko Haram is no doubt being "shaped" by ISIS, Khan said this week, and Jasmine Opperman, TRAC's director of African operations, added that Islamic State's objective to expand the caliphate will be well served by its allegiance with other groups.

"[Expansion] is not only achieved by means of gaining physical control in areas, but gaining support and loyalty from individuals, groups and organizations," she explained.

"A pledge of allegiance from Boko Haram will serve this objective."

Over three million people are believed to have been displaced by Boko Haram, with about half of those having fled Nigeria to neighbouring countries.

The terrorist group has garnered support through its determination to eradicate Nigerian democracy and replace it with an Islamic state guided by sharia law. The latest statistics suggest that violence associated with the organisation resulted in the deaths of more than 6,000 civilians in 2014. Its deadliest attack to date occurred in January 2015, when up to 2,000 people were killed in Baga, Borno state.