Relations were strained by a US drone strike in May that killed Afghan Taliban leader Mullah Akhtar Mansour as he was driving through Pakistan's Baluchistan province.
It claimed responsibility for the attack on the Army Public School in Peshawar, in northwest Pakistan in December 2014, in which at least 132 children, nine staff and several attackers were killed.
The mastermind of the terror attack on a school in Peshawar, Umar Mansour alias Khalifa Mansour alias Umar Naray, was killed in a United States drone strike in Afghanistan, Pakistani media organisation Dawn reports. However, Saifullah's death is yet to be confirmed. While one official said there were 90 per cent chances that he too had been killed along with Naray, another official said they were still trying to figure out whether he was there on the spot when the drone struck. The State Department had put the Tariq Gidar Group, a faction linked to the Pakistani Taliban, on its list of "Specially Designated Global Terrorists" in May. According to TTP the attack was intended as a strong warning to the Pakistani Army to not target the terror group. A security official at the time had denied there was any quid pro quo between the two countries.
Tehrik-e-Taliban Pakistan (TTP), the Pakistani Taliban branch, has yet to confirm Mansour's death as of the writing of this article.
Pakistan securities agencies regarded Umar as a major threat for Pakistan because of his violent and major terrorist attack across Pakistan.
Umar Mansoor claimed responsibility for planning the attack as well as a separate attack on Bacha Khan University in Charsadda on January 20 this year, in which 22 people, a lot of them students and teachers, were killed.
Mansour had fled to Afghanistan after a military-operation Khyber tribal region.