Parents of US female hostage devastated by death of 'devoted humanitarian who dedicated her youth to helping those in need'
A 26-year-old US woman held by Islamic State militants has been confirmed dead, her parents and the Obama administration have said.
The White House said Kayla Jean Mueller's family received a private message from her captors over the weekend and the information was authenticated by the US intelligence community. It was not immediately clear how and when she died.
"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. "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."
President Barack Obama said Ms Mueller, an aid worker who assisted humanitarian organisations working with Syrian refugees, "epitomised all that is good in our world".
"No matter how long it takes, the United States will find and bring to justice the terrorists who are responsible for Kayla's captivity and death," the president said.
The White House said Mr Obama had spoken to Ms Mueller's parents and offered his condolences and prayers.
She is the fourth American to die while being held by Islamic State militants. Three others - journalists James Foley and Steven Sotloff and aid worker Peter Kassig - were beheaded by the group.
Read more: Isis US hostage: Who is Kayla Jean Mueller?
Journalist Austin Tice, of Houston, Texas, disappeared in August 2012 while covering Syria's civil war. It is not clear what entity is holding him but it is not believed to be IS or the Syrian government, his family has said.
Ms Mueller was taken in August 2013 while leaving a hospital in Syria. Her identity was long kept secret out of fears for her safety.
On Friday, IS claimed she died in a Jordanian air strike. Jordan, which has launched a barrage of strikes on IS in recent days in retaliation for the killing of one of its pilots, disputed that report and the White House said at the time that it had seen no evidence to corroborate the claims.
Secretary of state John Kerry said the US was "unshaken" in its resolve to defeat IS, a group he called an "ugly insult to the civilised world".
Senator John McCain, who represents Ms Mueller's home state of Arizona, said, "The thoughts and prayers of the people of Arizona, America, and the civilised world are with the Mueller family at this terrible hour."
Her family said she graduated from Northern Arizona University in 2011. In December 2012, she traveled to the Turkish-Syrian border to work with several humanitarian groups, including Support to Life and the Danish Refugee Council.
She had also worked for aid groups in India, Israel and the Palestinian territories, as well as at an HIV/Aids clinic and women's shelter in Arizona.
Ms Mueller's parents released a letter she had written to them while in captivity.
The undated letter said she was "in a safe location, completely unharmed".
It added: "I am also fighting from my side in the ways I am able + I have a lot of fight left inside of me. I am not breaking down + I will not give in no matter how long it takes."