By Noah Rayman
February 6, 2015

The Islamic State in Iraq and Greater Syria has claimed that a female U.S. hostage was killed in the fierce Jordanian airstrikes that followed the execution of a Jordanian pilot held by ISIS.

The Islamist terror group said on Twitter that the woman, identified as humanitarian aid worker Kayla Mueller, was killed in the building where she was held outside the city of ar-Raqqah, according to the Site Intelligence Group.

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The claim has not been independently confirmed, and a spokeswoman for the National Security Council said in a statement that “We have not at this time seen any evidence that corroborates” the claim, the New York Times reports.

Jordanian government spokesman Mohammed al-Momani said authorities there were “highly skeptical” about the claim, the Wall Street Journal reports. “How could they identify Jordanian warplanes from a huge distance in the sky, and what was the American lady doing in a weapons warehouse? It’s part of their criminal propaganda.”

“Allah made their pursuit disappointed and deterred their cunning, and no mujahid was injured in the bombardment,” the ISIS message said. “It was confirmed to us the killing of an American female hostage by fire of the shells dropped on the site.”

Jordan launched a wave of new air strikes on Thursday after King Abdullah vowed to wage a “harsh” war against ISIS over the videotaped execution of Lt. Muath al-Kaseasbeh. The pilot was captured in Syria when his F-16 crashed in December, and a video posted online showed him burned alive in a cage.

Mueller, 26, disappeared in August 2013 in northern Syria, according to the Times, which said she is the only known remaining American hostage held by ISIS.

Write to Noah Rayman at noah.rayman@time.com.

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