Militants led by a former Pakistani Taliban representative pledged their loyalty to the Islamic State group in a video released this week. An army soldier, left, stands near a woman reading messages left by people in memory of the victims of the Taliban attack on the Army public school in Peshawar in December 2014. Reuters/Khuram Parvez

A video surfaced Saturday of a group claiming to be former Pakistani Taliban members pledging allegiance to the Islamic State group and beheading a man the militants claim is a Pakistani soldier, the Associated Press reported. Shahidullah Shahid, a former representative of the Pakistani Taliban, appears to lead the dozens of extremists, some of whom claim to be militant leaders in Pakistan and Afghanistan, AP said.

The Pakistani Taliban, or Tehrik-i-Taliban Pakistan, severed its relationship with Shahid in October after he and five other TTP figures swore loyalty to the Islamic State group in the Middle East, BBC News reported at the time. A senior TTP member said Shahid and the others defected to the Islamic State group because they lost faith in the Taliban’s longtime, shadowy leader Mullah Mohammad Omar, the news agency reported.

The video appeared on Islamic State-affiliated Twitter accounts and in forums frequented by jihadists, according to the SITE Intelligence Group, a U.S.-based monitoring group. SITE could not confirm where the video was shot, but said the group of militants appeared to be in a wooded area much like the mountainous region between Pakistan and Afghanistan where the Taliban is based.

If the video were legitimate, then it would mark a breakthrough in support for the Islamic State group in the region, where the Taliban and al Qaeda have historically been the dominant radical groups. The Islamic State group is based mainly in Iraq and Syria. It was largely unknown before last year, when it took over large swaths of land and imposed a strict interpretation of fundamentalist Islamic law amid the chaos of the Syrian Civil War.

A U.S.-led coalition of neighboring states began a campaign of airstrikes against the group in Iraq and Syria in June after the group threatened to overrun Baghdad and committed a number of atrocities, including the slaughter of ethnic and religious minorities in the region.

The Islamic State group and al Qaeda were once aligned, but the latter broke ties with the former last February over disagreements about methods and objectives, Reuters reported at the time. Since then, the Islamic State group has battled with al Qaeda’s official Syrian proxy, al Nusra Front.

TTP conducted the most deadly terrorist attack in Pakistan in years last month, when nine members stormed an army primary school in Peshawar and killed 145 people, mostly schoolchildren.