The parents of a US hostage Islamic State jihadists claim has been killed in an airstrike are "hopeful" she is still alive.
The militants say Kayla Jean Mueller was buried under rubble after a Jordanian warplane raid in the Syrian city of Raqa.
But Washington says it has no proof and refuses to confirm her death as the parents of the 26-year-old Arizona aid worker hold out hope.
"This news leaves us concerned, yet, we are still hopeful Kayla is alive. We have sent you a private message and ask that you respond to us privately," Carl and Marsha Mueller said in a statement published on NBC on Saturday.
They appealed for her safe return, saying they had previously been in touch with Islamic State militants following her kidnapping in August 2013.
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"You told us you treated Kayla as your guest, as your guest her safety and wellbeing remains your responsibility," they said.
Meanwhile, Jordan - still reeling from the brutal murder of one of its pilots by the jihadist group - also rejects the claim, calling it an "old and sick trick" to deter strikes.
"The plane from the crusader coalition bombed a position outside the city of Raqa after Friday prayers," IS said in a jihadist website statement.
"No fighter was wounded but we can confirm an American hostage was killed."
The claim came as Amman said dozens of its jet fighters had struck IS, widening their campaign from Syria to include targets in neighbouring Iraq.
Jordan is part of the international coalition battling the Sunni extremist group, which has seized swathes of territory in Syria and Iraq.
Mueller's family described her as "extremely devoted to the people of Syria".
She travelled to the country's border with Turkey in 2012 to help refugees fleeing the civil war and was captured after leaving a Doctors Without Borders hospital.
