The Islamic State of Iraq and the Levant armed group has claimed that a female US aid worker it held hostage was killed in a Jordanian airstrike in the Syrian city of Raqqa.
SITE Intelligence, a monitoring group, published a statement ISIL posted on social media on Friday.
Kayla Jean Mueller, 26, is understood to be the last U.S. hostage held by the terror group, which had been demanding $6.6 million - £4.3million - for her release.
Her death is not yet been verified by independent sources and could easily be a propaganda move by the terror group to lay blame for the woman's death at the door of Jordan.
The statement identified the woman as Kayla Jean Mueller and said she was killed during Muslim prayers - which usually take place around midday on Fridays - in airstrikes that targeted "the same location for more than an hour" in the group's main stronghold.
No ISIL fighters were killed in the airstrikes, the statement further claimed. It published photos allegedly of the bombed site, showing a severely damaged brown colored three-story building - but no images of Mueller.
American officials said they were urgently looking into the reports of Mueller's death.
Bernadette Meehan, the spokeswoman for President Barack Obama's National Security Council, said the White House has 'not at this time seen any evidence that corroborates' the claim.
'We are obviously deeply concerned by these reports,' she added.
White House spokesman Eric Schultz told reporters traveling with the president to Indiana on Friday that the U.S. does coordinate with the Jordanian air force on airstrikes.
He wouldn't say whether the U.S. was aware of the hostage's location.
If Mueller's death is confirmed, she would be the fourth American citizen to die while in the captivity of ISIL. Three other Americans, journalists James Foley and Steven Sotloff and aid worker Peter Kassig were beheaded by the group last year.