BEIRUT -- A statement attributed to the Islamic State of Iraq and Syria (ISIS) claimed that an American female hostage was killed in a Jordanian airstrike on Friday on the outskirts of the northern Syrian city of Raqqa, the extremist group's main stronghold.
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."
No ISIS militants 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 looking into the report. 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 Friday that the U.S. does coordinate with the Jordanian air force as they fly airstrikes. He wouldn't say whether the U.S. was aware of the hostage's location.
CBS News national security correspondent David Martin reports that a U.S. military officer said the building that ISIS claims the U.S. hostage was in "was a weapons storage facility, not anything that was assessed to be a hostage holding area."
"We would not strike a facility that was a known or possible hostage facility," the officer said.
The officer acknowledged that does not rule out the possibility that the American hostage could have been moved into the building either before or after the strike. He also confirmed that the targets went through the vetting process.
Jordanian government spokesman Mohammed al-Momani said Jordan was looking into the claim.
"But as a first reaction, we think it's illogical and we are highly skeptical about it," he said. "How could they identify a Jordanian warplane ... in the sky? What was the American lady doing in a weapons warehouse?"
"It's part of their criminal propaganda. They have lied that our pilot is alive and tried to negotiate, claiming he is alive while they had killed him weeks before," al-Momani added.
Jordan Foreign Minister Nasser Judeh took to Twitter to express his skepticsim of ISIS' claims:
The ISIS statement could not be independently verified. It appeared on a militant website commonly used by IS and was also distributed by ISIS-affiliated Twitter users.
Mueller, of Prescott, Arizona, had been working in Turkey assisting Syrian refugees, according to a 2013 article in The Daily Courier, her hometown newspaper. The 26-year-old told the paper that she was drawn to help with the situation in Syria.
"For as long as I live, I will not let this suffering be normal," she said. "It's important to stop and realize what we have, why we have it and how privileged we are. And from that place, start caring and get a lot done."
According to the local paper, Mueller had been working with the humanitarian aid agency Support to Life, as well as a local NGO that helped female Syrian refugees develop skills.
A 2007 article about Mueller from the same local newspaper said she was a student at Northern Arizona University and was active in the Save Darfur Coalition.
On Sunday, Obama said the U.S. was "deploying all the assets that we can" to find Mueller.
"We are in very close contact with the family trying to keep them updated," he said in an interview with NBC's Today Show. "Obviously this is something that is heart-breaking for the family and we want to make sure we do anything we can to make sure that any American citizen is rescued from this situation."
Mueller's identity had not been disclosed until now out of fears for her safety.
If her death is confirmed, she would be the fourth American to die while in the captivity of ISIS militants. Three other Americans, journalists James Foley and Steven Sotloff and aid worker Peter Kassig were beheaded by the group.
Jordan, which is part of a U.S.-led coalition bombing ISIS targets in Syria, stepped up its attacks after ISIS announced it had killed a captive Jordanian pilot. The Syrian government said Thursday that dozens of Jordanian fighter jets had bombed ISIS training centers and weapons storage sites. It did not say where the attacks occurred.
Video released earlier this week showed the pilot being burned to death in a cage, setting off a wave of anger in Jordan and the region, including from prominent Muslim clerics who condemned the execution method as a violation of Islamic principles.
The Jordanian military said that Jordanian jetfighters carried out "a series of attacks today and destroyed the targets and returned safely." It did not elaborate or give a location for the airstrikes.
But activists who monitor the Syrian conflict from inside the country said U.S.-led coalition planes hit several targets on the edges and outskirts of Raqqa, in quick succession on Friday.
A collective known as "Raqqa is Being Slaughtered Silently" said the planes targeted multiple IS positions and headquarters in the western and eastern countryside of Raqqa, sending columns of smoke into the sky. Explosions could be heard in the city. The collective said there were no recorded civilian casualties, and did not mention IS casualties.
The Britain-based Syrian Observatory for Human Rights said dozens of IS members were killed in coalition airstrikes that targeted a tanks-and-vehicles depot in the area of al-Madajen and at least six other IS positions, including a training camp and a prison.