Kayla Mueller, 26, an American humanitarian worker from Prescott, Ariz.
Mueller Family—Reuters
February 23, 2015 9:08 AM EST

An American who died while held captive by the militant group Islamic State of Iraq and Greater Syria (ISIS) wrote in her final letter to her family that she was “OK, healthy, remaining strong and being treated kindly.”

“Do not worry… I love you all,” Kayla Mueller wrote in the letter, revealed Monday on NBC’s Today show. “My heart longs to be with you all as… I have never felt before, but praise be to God you are in my dreams almost every evening and for just those brief moments in my sleeping conscious that we are together I am given a warmth.”

The Obama Administration confirmed earlier this month that Mueller, an aid worker who was 26, had died. ISIS said she was killed in a Jordanian airstrike, but U.S. officials haven’t confirmed that.

Read the full letter at NBC

Read next: What Kayla Mueller’s Life Reveals About Her Generation

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