Islamic State says Jordanian air strike kills US hostage
Islamic State (IS) militants claim that a US female hostage has been killed in a Jordanian air strike in Syria.
IS named the woman as aid worker Kayla Jean Mueller in statements online.
The group provided no other proof for the claim beyond pictures of the alleged site of the air strike, in Raqqa, the group's stronghold in Syria.
The White House said it was "deeply concerned" by the reports but that it has yet to verify them. Jordan has questioned the IS claims.
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.
The IS statement said 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.
Analysis: Aleem Maqbool, BBC News, Washington
There are many who have raised doubts about Islamic State's claim that Kayla Mueller was killed in a coalition strike in Raqqa - in an attack in which none of its own fighters died, it says.
Jordan has increased its participation in the bombing of the militant stronghold since one of its pilots was shown being burned to death by IS militants, and officials in Jordan insist they will keep up the pressure.
Saying a Western hostage has been killed by Jordan is being seen by some as an attempt to take the wind out of the sails of this renewed Jordanian resolve to fight the militants.
Claiming that the coalition killed Ms Mueller could also provide a convenient solution to Islamic State's problem of what to do with a female hostage, one they might not want to be shown killing in the same barbaric way as they have others.
Unfortunately the doubts about the veracity of the Islamic State claim will provide little comfort to Kayla Mueller's family and friends.
'Upping the ante'
The Jordanian foreign minister Nasser Judeh tweeted that the IS claims were "An old and sick trick used by terrorists and despots for decades: claiming that hostages [and] human shields held captive are killed by air raids."
Jordan said it carried out aerial bombardments on IS targets in Syria on Thursday, including on Raqqa.
The strikes were carried out in response to the killing of a Jordanian fighter pilot by IS militants.
A video of Moaz al-Kasasbeh being burned alive in a cage was posted online by IS earlier this week.
He was captured by militants in December after his F-16 fighter jet crashed in Syria. The video is believed to have been filmed on 3 January.
Foreign Minister Nasser Judeh said Thursday's strikes were "upping the ante" against IS.
Thousands rallied in Jordan's capital, Amman, on Friday morning in support of their government's military response.
Among those marching was Jordan's Queen Rania who told the BBC the killing had made Jordanians "determined to rid the world of this evil".