US confirms death of American ISIS hostage Kayla Mueller

President Barack Obama has released a statement confirming the death of an American hostage held by the Islamic State militant group.

Kayla Jean Mueller was a US aid worker from Prescott, Arizona.

Government officials reportedly told CNN that it's unclear how Mueller died.

Mueller's family released this statement (via NBC News): "We are heartbroken to share that we've received confirmation that Kayla Jean Mueller has lost her life. 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."

Mueller has been held in Syria since 2013. The Islamic State terror group, also known as ISIS, claimed that a Jordanian air strike killed her last week, but the group released contradictory evidence to back up the claim.

Here's the full statement from the White House: