A statement reportedly by the Islamic State (IS) group says a female American hostage has been killed in a Jordanian air strike outside the northern Syrian city of Raqqa.
The U.S. State Department said it could not confirm the claim in the statement, which appeared on a militant website commonly used by IS.
The White House said it was "deeply concerned" but that it had not seen "any evidence" to support the claim made by IS.
Jordan said it had conducted air strikes on IS positions in Syria but that the claims its air strikes killed an American hostage were a "PR stunt."
The statement identified the woman as Kayla Jean Mueller and said she died in an air strike during Friday Prayers.
It said air strikes struck the area "for more than an hour."
Photos of the alleged bombing site were included, showing a damaged three-story building.
The White House did not have any immediate comment.
Mueller is an aid worker whose identity had not been previously disclosed for safety reasons.