PESHAWAR, Pakistan (Reuters) - The alleged mastermind of the 2014 attack on a school in Pakistan in which more than 150 people died, most of them children, has been killed in an American drone strike in Afghanistan, the Pakistan military and sources in the Pakistani Taliban said.

General Asim Bajwa, director general of the Pakistani army’s media division, reported the death of Umar Narai, also known as Khalifa Umar Mansoor or Khalid Khurasani, in a message on Twitter.

U.S. Defense Department spokesman Peter Cook confirmed that U.S. forces carried out an air strike in Afghanistan’s eastern Nangarhar province on July 9, killing Umar Khalifa and four other militants.

Cook said Khalifa, a leader of the Tariq Gidar Group, was killed in a strike that targeted members of Islamic State-Khorasan Province. 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.

The Pakistani Taliban made no official comment. One senior member of the group said the movement had decided not to comment on the death until a successor had been chosen.

‎”It’s a huge loss to the small but most effective Taliban faction of Khalifa Umar Mansoor,” the commander said. There is no such prominent figure of his status to run his organization.”

The strike was the second in the space of two months against a senior insurgent leader close to the frontier between Afghanistan and Pakistan.

In May, Mullah Mohammad Akhtar Mansour, leader of the Afghan Taliban, was killed by a drone on the Pakistani side of the border.

The Pakistani Taliban is waging war against the Pakistani state and is separate from the Afghan Taliban. 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.

Umar Mansoor claimed responsibility for planning the attack as well as a separate attack on Bacha Khan University in Charsadda on Jan. 20 this year, in which 22 people, most of them students and teachers, were killed.