WASHINGTON - The parents of a US hostage who Islamic State jihadists claimed had been killed in an airstrike said on Friday they were "hopeful" she was still alive and appealed to her captors to contact them.
The militants said Kayla Jean Mueller had been buried under rubble after a raid by a Jordanian warplane in the Syrian city of Raqa, the extremists' self-proclaimed "capital."
But Washington said it had no proof to support the claim and refused to confirm her death as the parents of the 26-year-old aid worker from Arizona held out hope that she hadn't been killed.
"This news leaves us concerned, yet, we are still hopeful that 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 News.
They appealed for her safe return, and said they had previously been in touch with Islamic State militants following her kidnapping in August 2013.
"You told us that you treated Kayla as your guest, as your guest her safety and wellbeing remains your responsibility," they said.
"Kayla's mother and I have been doing everything we can to get her released safely." Meanwhile, Jordan - still reeling from the brutal murder of one of its pilots by the jihadist group - also rejected the claim, calling it an "old and sick trick" to deter coalition strikes.
"The plane from the crusader coalition bombed a position outside the city of Raqa after Friday prayers," IS said in a statement posted on jihadist websites.
"No fighter was wounded but we can confirm that an American hostage was killed in the strikes." 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 and imposed an extreme interpretation of Islam on the areas under its control.
Jordan had vowed an "earth-shattering" response after the jihadists burned one of its fighter pilots alive and released a video of the gruesome execution.
Washington stressed it had not seen any proof that Mueller, a 26-year-old aid worker from Arizona, had been killed. IS did not post any pictures of a body with its claim.