The Pentagon said US forces have killed Abu Sayed, the emir of the Afghan branch of ISIS at the group's headquarters in Kunar Province.
The US military said Sayed was killed in a drone strike on July 11.
Secretary of Defense James Mattis said his death represents a setback for ISIS-K.
Sayed is the third ISIS-K emir to be killed in the past year.
US successes against ISIS-K in Afghanistan
Pentagon: Sayed's death will 'significantly disrupt ISIS-K's expansion plans'
The Pentagon said the death of Sayed and other ISIS-K members in the strike "will significantly disrupt the terror group's plans to expand its presence in Afghanistan."
Mattis said: "Significance is, you kill a leader of one of these groups and it sets them back for a day, a week, a month, depending on who it is, what kind of people are below them…"
Sayed: The third ISIS-K emir to be killed
"Abu Sayed is the third ISIS-K emir we have killed in the last year, and we will continue until they are annihilated," said US Forces-Afghanistan Commander General John W. Nicholson.
"There is no safe haven for ISIS-K in Afghanistan," tweeted Nicholson.
In July 2016, ISIS-K emir Hafiz Sayed Khan was killed. A joint US-Afghan special forces raid killed emir Abdul Hasib in July 2016.
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US treats ISIS-K as bigger threat than other terror groups
Sayed's presence in Kunar indicates that ISIS-K's influence in Afghanistan is expanding.
Sayed's predecessors were both killed in the group's traditional stronghold of Nangarhar province.
In March 2017, Afghan and US forces launched an operation against ISIS-K.
It's important to note that US special forces serve a training and support role in other parts of Afghanistan. However, they are actively engaging with ISIS-K.
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