BEIRUT (AP) -- A purported statement by the Islamic State group 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 militant 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 Islamic State 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 the woman.

American officials said they were looking into the report. The White House said it did not have immediate comment.

The statement could not be independently verified. It appeared on a militant website commonly used by IS and was also distributed by IS-affiliated Twitter users.

Mueller is an aid worker whose identity was never disclosed out of concerns for her safety.

A family representative told The Associated Press last year that the 26-year-old was working with humanitarian groups in Syria when she was captured in 2013.

If her death is confirmed, she would be the fourth American to die while in the captivity of the Islamic State 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 Islamic State group targets in Syria, stepped up its attacks after IS announced it had killed a captive Jordanian pilot. The Syrian government said Thursday that dozens of Jordanian fighter jets had bombed Islamic State training centers and weapons storage sites. It did not say where the attacks occurred.

There was no word from the Jordanian government on whether its planes had struck Raqqa on Friday.