The brother of an American woman who was killed after spending months as a hostage of Islamic State militants says her situation worsened after the United States traded five Taliban commanders for a captive U.S. soldier.

Kayla Mueller's brother told NBC's "Today" in an interview that aired Monday that the militants' demands got greater after the May swap for Army Sgt. Bowe Bergdahl. Eric Mueller says that's when the militants "realized they had something."

He and his parents spoke with "Today" host Savannah Guthrie.

Kayla Mueller's death was confirmed Feb. 10 by her family and U.S. officials. The Islamic State group claimed she died in a Jordanian airstrike, but the Pentagon said it didn't know how she was killed.

The 26-year-old aid worker, who grew up in Prescott, Arizona, was captured in Syria in August 2013.