Story highlights The "Emir" of ISIS-K was killed on July 11, according to the Pentagon

Abu Sayed's death marks the third time an ISIS-K leader has been killed within a year

(CNN) The Pentagon said Friday that US forces have killed Abu Sayed, the leader of ISIS-Khorasan, the terror group's Afghanistan affiliate.

The "Emir" of ISIS-K was killed "in a strike on the group's headquarters in Kunar Province, July 11," Chief Pentagon spokesperson Dana White said in a statement.

US Navy Captain Bill Salvin, spokesman for US Forces Afghanistan provided additional detail of how Abu Sayed was killed. Salvin said he was killed in an airstrike by a US drone. The initial Pentagon statement described Sayed being killed in a "raid".

Secretary of Defense James Mattis told reporters on Friday that the death of a leader like Sayed "sets them back for a day a week, a month, it's about who it is and what kind of people are below them. It is obviously a victory on our side in terms of setting them back, it's the right direction."

Gen. John Nicholson, Commander, US Forces Afghanistan said in a statement, "This operation is another success in our campaign to defeat ISIS-K in Afghanistan in 2017. Abu Sayed is the third ISIS-K emir we have killed in the last year and we will continue until they are annihilated. There is no safe haven for ISIS-K in Afghanistan."

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