The United States says it has seen no evidence confirming claims by Islamic State (IS) militants that a U.S. woman held by the group was killed in a Jordanian air strike.
IS militants said the woman -- identified as Kayla Jean Mueller -- had been killed in the militants' stronghold of Raqqa in northern Syria during Muslim prayers on February 7.
It published photos purportedly of the bombed site, but offered no proof or images of Mueller.
The statement said no IS militants were killed in the air strikes.
U.S. National Security Council spokeswoman Bernadette Meehan said the White House was "deeply concerned," but had not seen any evidence to corroborate the claim.
Jordan dismissed the IS statement as "criminal propaganda."
The group's latest claim comes days after it released a video showing a captured Jordanian pilot being burned alive in a cage.
Mueller was the last-known U.S. hostage held by the militants, who control wide areas of Syria and Iraq.
The group has beheaded three other American, two British, and two Japanese hostages -- most of them aid workers or journalists -- in recent months.
Mueller was taken hostage while leaving a hospital in the northern Syrian city of Aleppo in August 2013.
A representative of Mueller's family said the family had no information on Islamic State's statement.
Jordan's King Abdullah has vowed to avenge the pilot's death and ordered a stepped-up military role in the U.S.-led coalition against the group.
Jordan said it had carried out a second straight day of air strikes on February 6 on IS positions.
Jordan is a major U.S. ally in the fight against militant Islamist groups.
It is home to U.S. military trainers bolstering defenses at the Syrian and Iraqi borders, and is determined to keep the jihadists in Syria and Iraq from crossing its frontiers.