PESHAWAR, Pakistan — The leader of the Pakistani Taliban was killed by a U.S. drone strike, an Afghan official said Friday.

Mullah Fazlullah Khorasani was Pakistan's most-wanted militant and blamed for attacks including a 2014 school massacre that killed 132 children and the 2012 shooting of schoolgirl Malala Yousafzai, who was later awarded the Nobel Peace Prize.

In March, the U.S. offered a $5 million reward for information on Fazlullah.

Afghan Defense Ministry spokesman Mohammad Radmanish told NBC News that Fazlullah died in a strike in the Marawaya district of the border province of Kunar.

Earlier, Lt. Col Martin O’Donnell, a spokesman for U.S. Forces in Afghanistan, said in a statement that U.S. forces had carried out an airstrike Thursday in Kunar "which targeted a senior leader of a designated terrorist organization."

The Kunar river in Afghanistan's Kunar province. John Moore / Getty Images file

Fazlullah's death could ease strained ties between Islamabad and Washington even as Afghanistan observes an unprecedented three-day ceasefire with the larger Afghan Taliban.

Pakistan is considered key to persuading Afghan Taliban leaders, who Washington believes shelter on Pakistani soil, to open negotiations to end the 17-year-old war in Afghanistan.

Prior to the Afghan Defense Ministry stating that Fazlullah had been killed, several members of the Pakistani Taliban told NBC News they had been unable to make contact with him and other senior commanders since receiving word of the strike.

They said they feared four other top commanders may also have been killed.

"Most of our people are seriously concerned ‎after they heard about the killing of our leader, but the top leadership is out of access," Pakistani Taliban commander Maulvi Obaidur Rahman told NBC News.

Like many other Pakistani militants, Khorasani had crossed into Afghanistan after the Pakistani army launched a major military offensive in the Swat Valley in 2009.

Mushtaq Yusufzai reported from Peshawar, Francis Whittaker from London, and Ahmed Mengli from Kabul.