The Pakistani cleric Maulana Sami ul-Haq, known as the Father of the Taliban, has been killed in the northern city of Rawalpindi.
Local media quoted his family members as saying that he was stabbed to death. But other reports say he was shot dead.
The motive for the attack is unclear.
Haq was the head of the Haqqania madrassa in the north of Pakistan, where many Taliban members - including the group's founder, Mullah Omar - had studied.
What is known about Friday's attack?
There are still conflicting reports of exactly how Haq was killed.
The cleric's son said his father was stabbed "multiple times" in the house he owned in Rawalpindi.
"He was resting in his room during Asr time when his driver-cum-guard went out for 15 minutes," Maulana Hamid ul-Haq was quoted as saying by Pakistan's Geo TV.
"When he returned, he found Maulana Sami ul-Haq dead in his bed and his body covered in blood."
Meanwhile, Haq's nephew Mohammad Bilal told Reuters his uncle was found with stabbing and gunshot wounds in his house on Islamabad's outskirts.
No group has so far claimed responsibility for Friday's attack.
Afghan officials had recently asked the cleric, believed to have been in his 80s, to help convince the Taliban to begin peace negotiations.
He was a former senator who ran a faction of the religious Jamiat Ulema-e-Islam party - and was close to Prime Minister Imran Khan's PTI party.
Mr Khan is currently on an official visit to Beijing, but his office said in a statement that he condemned the killing and had ordered an investigation.
The cleric's death comes at a time of turmoil in Pakistan, where protests have broken out in a number of cities after the acquittal of a Christian woman sentenced to death on blasphemy charges.
Haq had thousands of followers among his students, as well as Afghan and local Taliban members. The BBC's M. Ilyas Khan says there are fears that his killing may cause further trouble on the streets.