"Our leader, Omar Khalid Khorasani, was wounded in one of the recent drone strikes in Afghanistan. He was wounded badly, and today he was martyred," Asad Mansoor, a Jamaat-ul-Ahrar spokesman, said by telephone.
The killing comes ahead of American Secretary of State Rex Tillerson's visit next week and is likely to further ease tensions between the often-wary allies, as Islamabad has been asking Washington for years to target militants who attack inside Pakistan and then hide over the border in Afghanistan.
A splinter group of the Pakistani Taliban, Jamaat-ul-Ahrar has in the past also backed Middle East-based ISIS and has increasingly targeted religious minorities in Pakistan.
(Writing by Kay Johnson; Editing by Nick Macfie)