The parents of a US hostage, who Islamic State jihadists said died in a coalition airstrike, have said they were "hopeful" she was still alive and asked her captors to contact them.
IS said Kayla Jean Mueller had been buried under rubble after a raid by a Jordanian warplane in the Syrian city of Raqqa, but Washington said it had no proof to support the claim.
The parents of the 26-year-old humanitarian worker appealed to her kidnappers to get in touch with them.
"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.
The family said they had been in touch with her captors in the past and made a public appeal yesterday for her safe return.
"You told us that you treated Kayla as your guest, as your guest her safety and wellbeing remains your responsibility," according to the statement.
"Kayla's mother and I have been doing everything we can to get her released safely. At this time we ask you, who are holding Kayla, to contact us privately."
Ms Mueller, a humanitarian worker from Arizona, had travelled to the Turkish-Syrian border in December 2012 aiming to help Syrian refugees fleeing civil war.
The American aid worker was kidnapped in Aleppo, Syria in August 2013 after she left a Doctors Without Borders hospital.
The family said she has been held by Islamic State militants since then.
The jihadists' claim of her death came as Jordan said dozens of its jet fighters had struck IS, widening their campaign from Syria to include targets in neighbouring Iraq.
Jordan, still reeling from the murder of one of its pilots by IS, rejected the claim that Ms Mueller had been killed as an "old and sick trick" to deter coalition strikes.
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.
A Jordanian army source said today the United Arab Emirates were sending a squadron of F16 jet fighters, which would be based in Jordan, to help intensify airstrikes against IS militants to avenge the death of its pilot.
"They will be based in Jordan. This is a big boost and will be helping our brothers shorten their flying distances and intensify strikes against the militants from Jordan," an army source told Reuters news agency.
Jordan carried out a third straight day of air strikes on IS targets in response, it said, to the group's killing of a captive Jordanian pilot.
It said some of the targets were in the Syrian city of Raqqa but gave no other details.
Jordan began on Thursday what it called an "earthshaking" response to the death of the pilot.
