US aid worker Kayla Mueller has died while being held hostage by Isis, her family and the White House has confirmed.
Last week Isis claimed the 26-year-old, from Arizona, had died in a Jordanian air strike, but that was contested by Jordan.
However, the US government said that her death had now been authenticated by intelligence officials.
Mueller, seized while leaving a hospital in Syria in August 2013, is thought to be the last American hostage held by Isis.
In a statement, her parents Carl and Marsha Mueller said the family was "heartbroken" by her death.
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.
In a letter to her father on his birthday in 2011, Kayla wrote:
'I find God in the suffering eyes reflected in mine. If this is how you are revealed to me, this is how I will forever seek you.'
'I will always seek God. Some people find God in church. Some people find God in nature. Some people find God in love; I find God in suffering. I've known for some time what my life's work is, using my hands as tools to relieve suffering.'
Kayla was drawn to help those displaced by the Syrian civil war. She first travelled to Turkey in December, 2012 to provide humanitarian aid to Syrian refugees. She told us of the great joy she took in helping Syrian children and their families.
We are so proud of the person Kayla was and the work that she did while she was here with us. She lived with purpose, and we will work every day to honor her legacy.
Our hearts are breaking for our only daughter, but we will continue on in peace, dignity, and love for her.
We remain heartbroken, also, for the families of the other captives who did not make it home safely and who remain in our thoughts and prayers. We pray for a peaceful resolution of the conflict in Syria.
The White House said it learned of Mueller's death with "profound sadness".
Kayla dedicated her life to helping others in need at home and around the world. In Prescott, Arizona, she volunteered at a women's shelter and worked at an HIV/Aids clinic. She worked with humanitarian organisations in India, Israel, and the Palestinian territories, compelled by her desire to serve others. Eventually, her path took her to Turkey, where she helped provide comfort and support to Syrian refugees forced to flee their homes during the war. Kayla's compassion and dedication to assisting those in need shows us that even amongst unconscionable evil, the essential decency of humanity can live on.
Kayla represents what is best about America, and expressed her deep pride in the freedoms that we Americans enjoy, and that so many others strive for around the world. She said: 'Here we are. Free to speak out without fear of being killed, blessed to be protected by the same law we are subjected to, free to see our families as we please, free to cross borders and free to disagree. We have many people to thank for these freedoms and I see it as an injustice not to use them to their fullest.'
Kayla Mueller used these freedoms she so cherished to improve the lives of others. In how she lived her life, she epitomised all that is good in our world. She has been taken from us, but her legacy endures, inspiring all those who fight, each in their own way, for what is just and what is decent. 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.
[Isis] is a hateful and abhorrent terrorist group whose actions stand in stark contrast to the spirit of people like Kayla. On this day, we take comfort in the fact that the future belongs not to those who destroy, but rather to the irrepressible force of human goodness that Kayla Mueller shall forever represent.
Mueller's family also today released a letter the aid worker wrote while in captivity - thought to be her last correspondence - and passed on by one of her former cellmates.
In it, she wrote:
I have been shown in the darkness, light, and have learned that even in prison, one can be free. I am grateful. I have come to see that there is good in every situation, sometimes we just have to look for it.