Mullah Abdul Manan Niazi told the BBC that Mullah Mansour, who was appointed Thursday to succeed Mullah Mohammed Omar, was not chosen "by all Taliban."
"According to Islamic rule and principles, when a leader dies, a [council] is called, then its leader it appointed," Niazi said, arguing that that had not taken place and therefore went against Sharia law.
Mullah Omar, founder and spiritual leader of the movement that ruled most of Afghanistan in the 1990s until its overthrow by NATO-led forces in 2001, was confirmed this week to have died two years ago.
The Afghan Presidential Administration claimed that Omar died in the Pakistani city of Karachi in April 2013, while official Pakistan has repeatedly denied that Omar was in the country.
The British broadcaster said some Taliban figures accused pro-Pakistani factions of imposing Mullah Mansour, who supported peace talks with the Afghan government.
The Pakistani Foreign Ministry said on Thursday it was suspending the second round of negotiations between Kabul and the Taliban, scheduled for Friday, in view of the recent news.
