Maulana Sami ul Haq, chief of Jamiat Ulema-e-Islam Pakistan, has been killed in an attack in Pakistan's Rawalpindi city, Pakistan's Geo News reported. Police officials have said they are investigating.
Human Rights Minister Shireen Mazari said the brutal murder of Maulana Samiul Haq was "utterly condemnable".
Haq's son, Hamidul Haq, said his father was killed on Friday.
Maulana Mehmoodul Haq Haqqani, another brother, was professor of chemistry in University of Peshawar where he was called Father of Chemistry and later he represented Pakistan as deputy ambassador in Saudi Arabia. Some local media said ul-Haq was in the neighbouring city of Rawalpindi when he was shot and killed.
Hundreds of protesters took to the streets near the northwestern town of Mardan near Haq's seminary, setting a highway toll station on fire.More news: Protests rage in Pakistan after woman acquitted of blasphemy
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Haq's seminary has continued to thrive in Pakistan, including being allocated funding in the budgets of the provincial government, which is headed by Imran Khan's Pakistan Tehreek-e-Insaf (PTI) party.
Sami ul Haq was known as the spiritual father of Taliban.
Influential religious scholar Maulana Samiul Haq was born to Maulana Abdul Haq, a prominent cleric, on December 18, 1937 in Akora Khattak of Nowshera district in Khyber-Pakhtunkhwa.
The Chief of Army Staff, General Qamar Javed Bajwa has strongly condemned the assassination of renowned religious scholar and political leader Maulana Samiul Haq.
Prime Minister Imran Khan, who is now in China for an official visit, said the country had been deprived of an important religious leader whose services would always be remembered.