The octogenarian, who was known for his Afghan Taliban support, was found dead at his residence in city of Rawalpindi.

A Pakistani political and religious leader has been killed by unknown attackers at his residence in the northern city of Rawalpindi, according to family members and officials.

Sami-ul-Haq, 80, was stabbed to death in his bed on Friday, his son Hamidullah told local television news channel ARY by telephone.

“He was resting in his room … He had been ill, and was a heart patient,” said Hamidullah.

“His guard had left the room for 15 minutes, when he returned he found Maulana [Haq]’s body covered in blood in his bed.”

Saeed-ur-Rehman Sarwar, a leader of Haq’s JUI-S political party, also confirmed the killing.

“Maulana Sami-ul-Haq has been killed,” he said from outside the government hospital where his body was taken.

Who was Sami-ul-Haq?

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A divisive figure, Haq was known as the “Father of the Taliban”.

He led the ideological fight that led to the formation of the mujahideen force that first fought the Soviet invasion of Afghanistan, and later morphed into the Afghan Taliban.

Haq was the chief of the Darul Uloom Haqqania seminary in the northern Pakistani town of Akora Khattak, the alma mater of several senior leaders of the Afghan Taliban, including former chief Mullah Omar and Mullah Akhtar Mansour.

He openly backed the Afghan Taliban in its fight against the Afghan government and the United States-led NATO forces in Pakistan’s northwestern neighbour.

Within Pakistan, Haq was considered a hardline right-wing religious leader, but his party contested elections, rather than outright backing armed struggle against the state, as was undertaken by the Pakistan Taliban.

He was a former senator, having served in Pakistan’s upper house of parliament for multiple terms in the 1980s and 1990s, and again from 2003 to 2009.

Prime Minister Imran Khan, in China on a state visit, issued a statement condemning the attack on Haq.

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“With Maulana Sami-ul-Haq’s martyrdom, the country has lost an important religious and political leader,” he said on Friday.

The prime minister’s Pakistan Tehreek-e-Insaf (PTI) entered into a pre-election alliance with Haq’s JUI-S, although the two later parted ways before Pakistan’s July general vote, which Khan’s party swept.

In 2016, the PTI had also issued a grant of 300 million rupees ($2.24m) to the Darul Uloom Haqqania seminary, with Khan arguing that the seminary sector needed to be brought closer in line with Pakistan’s education policies and syllabi.

Reporting by Asad Hashim, Al Jazeera’s digital correspondent in Pakistan. He tweets @AsadHashim