The family of American Isis hostage Kayla Jean Mueller has refused to give up hope that she is still alive after the militant group yesterday claimed she was killed by a Jordanian airstrike.
Carl and Marsha Mueller have reached out to "those in positions of responsibility for holding Kayla" to get in touch privately, according to a statement.
They said: "This news leaves us concerned, yet, we are still hopeful that Kayla is alive.
"You told us that you treated Kayla as your guest, as your guest her safety and well-being remains your responsibility."
Isis has said she was killed in bombing by Jordanian fighter jets after the Middle Eastern state stepped up its military involvement in the wake of of the release of a video this week of pilot Muath al-Kasasbeh's murder.
US officials have said they are unable to confirm that Mueller had been killed, and Jordanian leaders have questioned the claims.
In pictures: Anti-Isis protests in Jordan
In pictures: Anti-Isis protests in Jordan
1/15 Amman, Jordan
Members of Jordan's Al Assaf tribe burn a ''Wanted Dead'' poster of Islamic State leader Abu Bakr al Baghdadi at a rally
2/15 Amman, Jordan
Jordanian protesters carry an effigy of leader of the militant Islamic State Abu Bakr al-Baghdadi, during a march after Friday prayers in downtown Amman
3/15 Amman, Jordan
Jordanian Queen Rania (C) holds a placard during a demonstration to express solidarity with the pilot murdered by the Islamic State
4/15 Amman, Jordan
A protester dressed in a Jordanian flag joins others as they hold up pictures of Jordanian King Abdullah and Jordanian pilot Muath al-Kasaesbeh, while chanting slogans during a march against Islamic State
5/15 Amman, Jordan
Jordanians hold banners shouting slogans during a demonstration to express their solidarity with the pilot murdered by the Islamic State
6/15 Amman, Jordan
Jordanians carry banners and pictures of executed Jordanian pilot Muath al-Kassasbeh while shouting slogans against the group calling themselves the Islamic State, during a march after noon pray in downtown Amman
7/15 Amman, Jordan
Protesters hold up pictures of Jordan's King Abdullah and pilot Muath al-Kasaesbeh as they chant slogans during a rally in Amman to show their loyalty to the King and against the Islamic State
8/15 Amman, Jordan
Jordanians chant slogans to show their support for the government against terror during a rally
9/15 Amman, Jordan
Jawdat al-Kaseasbeh, a brother of slain Jordanians pilot Muath al-Kaseasbeh, reacts to people gathering to show their support for the government against terror during a rally
10/15 Amman, Jordan
A Jordanian protester kisses a poster bearing the image of Jordanian pilot Muath al-Kasaesbeh during a rally to show their loyalty to King Abdullah and against the Islamic State
11/15 Amman, Jordan
A Jordanian shouts slogans during a rally against the Islamic state group and in reaction to the burning alive of Jordanian pilot Maaz al-Kassasbeh by the group's militants
12/15 Amman, Jordan
Jordanians carry pictures of pilot Maaz al-Kassasbeh at a protest against Islamic State
13/15 Amman, Jordan
Supporters and family members of Jordanian pilot Lt. Muath al-Kaseasbeh express their anger at his murder at the tribal gathering chamber in Amman, Jordan
14/15 Aye Village, Karak, Jordan
The King of Jordan, Abdullah II (L), embracing Safi al-Kassasbeh (R), the father of the recently executed Jordanian pilot
15/15 Aye Village, Karak, Jordan
Jordan's Queen Rania offers her condolences to the family of Jordanian pilot Muath al-Kasaesbeh, at their family home of Muath
REUTERS/Petra News Agency
Aid worker Mueller was taken captive in August 2013 while working at a hospital with Spanish Doctors Without Border in the Syrian city of Aleppo.
A year later it was reported that Isis was demanding equivalent to 4.3m for her release, and had provided a proof-of-life video.
She was the last known US hostage of Isis, following the execution of three others in 2014, as well as two British and, more recently, two Japanese hostages.
Most of these were aid workers or journalists.
Mueller, from Prescott, Arizona, was resolved to helping others at an early age, according to her family.
They said: "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'."
An award-winning volunteer, she graduated from Northern Arizona University in 2009 and went on to work for humanitarian aid groups in India, Palestine, and Israel before returning to the US to work at an HIV/AIDS clinic and volunteer at a woman's shelter.
She moved 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.
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.
Additional reporting by ReutersReuse content