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By Mushtaq Yusufzai

PESHAWAR, Pakistan — The Afghan Taliban announced a reshuffle of its senior leadership in part to shore up the fractured organization fighting ISIS encroachment in parts of the country.

Taliban spokesman Qari Yousaf Ahmadi told NBC News on Tuesday that the group had appointed the eldest son and the brother of the Taliban's late founder, Mullah Omar, as members of their powerful Leadership Council.

Mullah Akhtar Mohammad Mansour was named the head of the militant organization soon after it emerged in July that Omar had actually been dead for two years. Omar's eldest son Yaqoob and younger brother Manan both had been seen as his possible successors.

Related: Beheadings Raise Specter of ISIS on March in Afghanistan

The announcements came as ISIS showed signs of making inroads in Afghanistan. In December, ISIS released a highly produced video calling the Taliban deviant.

An ISIS district leader at an undisclosed location in Afghanistan's Kunar province in July 2015.GHULAMULLAH HABIBI / EPA

Another commander who operated in Kunar province in the east of the country said their main enemy was ISIS, not the U.S. or their allies which have been trying to root out the Taliban since helping topple the group from power in 2001.

"Daesh is a real threat as they are snatching our people and increasing its writ in Afghanistan," the commander told NBC News on condition of anonymity, using another name for ISIS.

The announcements came amid growing uncertainty about whether new leader Mansour was even alive, he added.