White House officials say they have not seen any evidence to confirm reports by the Islamic State (IS) militant group that an air strike killed a US hostage.

The group says a female hostage, Kayla Jean Mueller, was killed when Jordanian jets bombed a house on the outskirts of their Syrian stronghold, Raqqa.

No proof has been offered other than a photo of a ruined building.

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

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.

According to IS, she was killed in the building where she was being held. It did not provide images of a body.

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 but added that officials had seen no evidence to corroborate the IS report.

(BBC)