The parents of an American humanitarian worker held hostage by Islamic State since August 2013 said on Friday they are hopeful she is still alive, after the group said she was killed in a bombing by Jordanian fighter jets.
Carl and Marsha Mueller, the parents of Kayla Jean Mueller, asked the Islamic State group to contact them privately, according to a statement released by a family representative.
"This news leaves us concerned, yet, we are still hopeful that Kayla is alive," they said in the message.
In a message directed to "those in positions of responsibility for holding Kayla," they said: "You told us that you treated Kayla as your guest, as your guest her safety and well-being remains your responsibility."
Mueller was the last-known American hostage held by Islamic State, which controls wide areas of Syria and Iraq. The militant Islamist group has beheaded three other Americans, two Britons and two Japanese hostages - most of them aid workers or journalists - in recent months.
U.S. officials said they could not confirm that Mueller had been killed. Jordanian leaders have questioned the group's claims.
Kayla Mueller, from the small city of Prescott about 100 miles (160 km) north of Phoenix, felt compelled to help others from an early age, according to a statement from the family.
"When asked what kept her going in her mission, she said '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'," the statement said.
As a high school student at Tri City College Prep, she received several awards, in part for her volunteering with groups like AmeriCorps and Big Brothers Big Sisters, the statement said.
She graduated from Northern Arizona University in 2009 and went on to work for humanitarian aid groups in northern India, Palestine, and Israel before returning to Arizona to work at an HIV/AIDS clinic and volunteer at a woman's shelter, it said.
Mueller relocated to the Turkish-Syrian border in December 2012 to help Syrian refugees, working with the Danish Refugee Council and the aid group Support to Life. She was taken by Islamic State while leaving a hospital in the northern Syrian city of Aleppo in August 2013.
Her parents said they had previously remained silent about her capture "out of concern for Kayla's safety," and to abide by the group's warnings.