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The parents of a US hostage who Islamic State (IS) militants say was killed by a Jordanian air strike in Syria have asked the group to make contact, the BBC reported.

They said in a statement they believed aid worker Kayla Jean Mueller was still alive and urged the militants to treat her as a "guest."

White House officials say they have seen no proof she was killed.

IS released images of a ruined building where it says she died but no images of the aid worker herself.

It said that Jordanian jets had bombed the building on the outskirts of their Syrian stronghold, Raqqa.

Jordan, which carried out air strikes on IS targets in Syria on Thursday, dismissed the reports as propaganda.

Mentioning previous communications with IS in their statement, Ms Mueller's parents said they had decided to break their public silence at news of reports of their daughter's death.

"This news leaves us concerned, yet, we are still hopeful that Kayla is alive," they said.

"We have sent you a private message and ask that you respond to us privately...

"You told us that you treated Kayla as your guest, as your guest her safety and wellbeing remains your responsibility."

A graduate of Northern Arizona University, Ms Mueller, 26, first came to the Turkish/Syrian border in 2012 to work with refugees.

She was abducted while working in Aleppo, Syria the following year.

If her death is confirmed, she would be the fourth American to die while being held by IS. Journalists James Foley and Steven Sotloff, and aid worker Peter Kassig, were beheaded by the group.

A spokeswoman for US President Barack Obama's National Security Council said the US was "deeply concerned" by the reports of her death but added that officials had seen no evidence to confirm the IS report.