Unknown motorcyclists opened indiscriminate fire on the vehicle of the JUI-S chief.
The JUI-S chief was being shifted to DHQ Hospital before he succumbed to his wounds.
However, initial reports had said that Haq had been shot. The prime minister's aide on political affairs, Naeemul Haq, said the religious scholar's martyrdom was a huge tragedy.
"In our tradition, a teacher is like a father, like a spiritual leader", Haq told Reuters in 2013.
As leader and administrator of Darul Uloom Haqqania University, Haq is credited with producing thousands of future adherents for the Taliban. A member of Jamiat Ulema-e-Islaml Pakistan has confirmed Sami ul Haq's assassination.
He had been aligned with the ruling Pakistan Tehreek-i-Insaf for the July 25, 2018 election. Haq's nephew Mohammad Bilal said his uncle was found with stabbing and gunshot wounds in a house he owns in an upscale area on Islamabad's outskirts.
Government Plans £400m Tax Raid on Tech Giants
Almost half of the reforms will only affect the most well-off 10 per cent as tax changes become "even more regressive". Mr Mackay told MSPs he would set out his intentions in the draft Scottish Budget on December 12.
No individual or group has so far claimed responsibility behind the assassination of Maulana Samiul Haq. The army chief also extended his condolences to the bereaved family.
The President paid tributes to Maulana Sami-ul-Haq's religious, social and political services.
Khan, now on an official visit to Beijing, condemned the killing and ordered an investigation, his office said in a statement. The cleric's son, Hamid-ul-Haq, said that his father was stabbed multiple times inside his bedroom at his residence in Bahria Town.
Punjab Chief Minister Usman Buzdar also denounced the assassination and sought a report from the Inspector General of Punjab Police.
State Minister for Interior Shahryar Afridi condemned the slaying in a statement and said he "shared the pain" of his family. "He was no longer alive", Hamid said while talking to Geo News.