A video was posted Tuesday by the Islamic State showing the beheading of Sotloff in response to continued U.S. military action in Iraq.
"For so many who worked so long to bring Steven and other Americans home safely," Kerry said Wednesday, "this was not how the story should've ended."
"The U.S. government used every military, diplomatic, and intelligence tool we have" to bring Sotloff home. Despite the failure to do so, Kerry emphasized "That effort continues, and our prayers remain -- as they always are -- with the families of all hostages who remain trapped in Syria today."
Kerry described Sotloff as "a driven and courageous journalist," whose "reporting was as empathetic as his killers are evil."
Kerry offered his condolences to Steven's family, acknowledging that his mother's "heartbreaking video plea spoke to every single parent who has ever worried about a son or daughter who goes to dangerous places to do the work they love."
Sotloff's mother, Shirley Sotloff, appealed to IS leader Abu Bakr al-Baghdadi last week to spare her son's life, delivering a recorded video message that was aired by Al Arabyia news station. In the video, she pleaded, "As a mother, I ask your justice to be merciful and not punish my son for matters he has no control over."
The Secretary of State concluded his message with a warning to the Islamic State:
"When terrorists anywhere around the world have murdered our citizens, the Untied States held them accountable, no matter how long it took. And those who have murdered James Foley and Steven Sotloff in Syria should know that the United States will hold them accountable too, no matter how long it takes."
Sotloff, 31, was abducted last year while working as a freelance journalist in Syria.