According to the AP, the White House confirmed Mueller's family "received a private message from her captors over the weekend and the information contained in that communication was authenticated by the U.S. intelligence community."
The Islamic State is claiming that Mueller died during a Jordanian airstrike last week in Raqqa, the group's "de facto capital," according to the Post. ISIS operatives had previously demanded $6.6 million in exchange for her release.
"We are heartbroken to share that we've received confirmation that Kayla Jean Mueller, has lost her life," Carl and Marsha Mueller said in a statement Tuesday. "Kayla was a compassionate and devoted humanitarian. She dedicated the whole of her young life to helping those in need of freedom, justice, and peace."