An American female hostage has been killed in a Jordanian air strike in Syria, Islamic State (ISIS) militants have said.

ISIS 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 ISIS claims.

A graduate of Northern Arizona University, Kayla Jean 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 ISIS statement said she was killed in the building where she was being held. It did not provide images of a body.

If Kayla Jean Mueller’s death is confirmed, she would be the fourth American to die while being held by ISIS. Journalists James Foley and Steven Sotloff, and aid worker Peter Kassig were beheaded by the group.

The Jordanian foreign minister Nasser Judeh tweeted that the ISIS 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 ISIS targets in Syria on February 5, including on Raqqa.

The strikes were carried out in response to the killing of Jordanian fighter pilot Moaz al-Kasasbeh by ISIS militants.

A video of Moaz al-Kasasbeh being burned alive in a cage was posted online by ISIS earlier this week.

Moaz al-Kasasbeh was captured by militants in December after his F-16 fighter jet crashed in Syria. The video is believed to have been filmed on January 3.

Foreign Minister Nasser Judeh said Thursday’s strikes were “upping the ante” against ISIS.

Thousands rallied in Jordan’s capital, Amman, on February 6 in support of their government’s military response. Among those marching was Jordan’s Queen Rania.

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