Abdul Qayum Zakir had disagreed with the appointment of Mullah Akhtar Mansoor as leader of the Taliban following the death of the movement's one-eyed founder, Mullah Mohammad Omar.
Two Taliban members, Mohammad Ghaus, a foreign minister in the Taliban's 1996-2001 regime, and ruling council member Mullah Gul Rahman Saleem told The Associated Press that Zakir had recently pledged allegiance to Mansoor.
Mansoor had led the movement in Omar's name for more than two years after he died. Kabul's announcement of Omar's death elevated Mansoor to the leadership, but led to deep mistrust among some at the top of the insurgent movement who felt betrayed.
The announcement of Omar's death also derailed a peace process that has yet to be revived. The Taliban recently announced they would not attend direct talks with Afghan government representatives, which Kabul officials had said would take place in early March.
Also Read
This appears to be an attempt to strengthen his position ahead of any peace dialogue, consolidating battlefield gains made after the international combat mission ended in 2014 and left Afghan forces to fight largely alone for the first time in the war's 15 years.
Zakir, a former Taliban military commission leader who spent time in Guantanamo Bay prison after the 2001 US invasion toppled the Taliban regime, held a number of senior roles within the group, both during its rule of Afghanistan and after it went into exile in neighboring Pakistan.
His power base is in southern Helmand province, where most of the world's opium is produced, and where Mansoor is believed to control the bulk of the smuggling routes.