Pakistani Taliban leader Mullah Fazlullah has been killed in a US-Afghan air strike in Afghanistan, a senior Afghan Defense Ministry official said on Friday, a killing likely to ease tension between the United States and Pakistan.

The US military said in Washington on Thursday it had carried out a strike aimed at a senior militant figure in the eastern Afghan province of Kunar, which is on the Pakistani border, and one US official said the target was believed to be Fazlullah.

Fazlullah was Pakistan's most-wanted militant, notorious 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.

"I confirm that Mullah Fazlullah, leader of the Pakistani Taliban, has been killed in an joint air operation in the border area of Marawera district of Kunar province," Mohammad Radmanish, spokesman for Afghan defense ministry, told Reuters, adding the air strike was carried out at about 9 a.m. on Thursday.

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.

In March, the United States offered a $5 million reward for information on Fazlullah.

A member of the Pakistani Taliban told Reuters by telephone on Friday the group was trying to get word from Afghanistan, where most of the Pakistani Taliban fighters are now based.

"We have been hearing since early Friday that our Emir(leader) was martyred along with four other militant commanders in Marawar area of Kunar. They were staying at a house when a drone fired missiles and martyred them," said Taliban member Maulvi Abdur Rasheed.

Fazlullah emerged as an Islamist leader in the Swat Valley, northwest of the Pakistani capital of Islamabad, more than a decade ago. He was known as "Mullah Radio" for his fiery broadcasts.

He was reviled in Pakistan for the 2014 assault on an army-run school in the city of Peshawar in which Pakistani Taliban gunmen killed at least 132 children.

He is also believed to have ordered the 2012 shooting of then-15-year-old Yousafzai over her advocacy of girls' education.

The Pakistani Taliban have waged a decade-long insurgency seeking to establish a harsh interpretation of Islamic rule but most of their fighters have now fled to Afghanistan.

They are separate from the Afghan Taliban who ruled Afghanistan for five years before being ousted in a 2001 U.S.-led military action.

Washington and Kabul accuse Pakistan of harboring Afghan Taliban and the allied Haqqani network, which Islamabad denies. Islamabad says the Pakistani Taliban maintain sanctuaries in Afghanistan.