In a statement issued on Wednesday, Mohammad Khurasani, a spokesman for the Tehreek-e-Taliban Pakistan (TTP), confirmed the death of Khalifa Umar Mansoor. The militant group, however, did not say when or where Mansoor had been killed.
Khurasani also announced that "Khalifa Usman Mansoor will replace him in Darra Adam Khel and Peshawar."
The Pakistani military or government has yet to comment.
The statement came two days after drone strikes carried out by the United States in the tribal regions along the border with Afghanistan reportedly killed more than two dozen militants. Senior Pakistani officials say the drone strike violates the country’s sovereignty.
In December 2014, the Mansour-led faction of the TTP stormed an army-run school in Peshawar and killed about 150 people, including 134 students. The massacre shocked and outraged a country already scarred by nearly a decade of attacks.
The raid prompted Pakistan to set up military courts for terrorism and lift a 2008-moratorium on the death penalty. The massacre also spurred the military to intensify an operation in the tribal areas, where militants had previously operated with impunity.
In January 2016, a group of gunmen from the same faction launched an attack on a university in the northwestern city of Charsadda, where 21 people were killed.
After both attacks, Mansoor issued videos vowing to target schools across Pakistan.
Pakistan has been engaged in a major offensive against militant hideouts across the troubled northwestern tribal regions since June 2014 to quell violence that has been raging unabated over the past few years.