U.S. government officials report that Kayla Mueller, the American who was kidnapped while doing relief work with Syrian refugees, was repeatedly raped by the top leader of the self-proclaimed Islamic State.

ABC News writes that these details about Mueller's treatment, "which involved torture since the beginning of her one-and-a-half years of captivity, her family has been told by the FBI — shatter rumors spread by some officials that she had cooperated or was a willing spouse, which has deeply upset her family and many inside her case."

ISIS claimed in February that Mueller was killed in an airstrike, but the U.S. government has not established how she died.

Her parents confirmed they had been told about her ordeal, NPR's Kirk Siegler tells our Newscast unit.

"According to a spokesman for Kayla Mueller's parents, the family learned in June from the U.S. government about her treatment while in captivity," Kirk notes.

"U.S. officials say she was held for a time by Abu Sayyaf, a former ISIS financier and his wife. According to witnesses, from his compound, she was taken as a 'wife' by the top leader of the Islamic State, Abu Bakr Baghdadi, who repeatedly raped her.

"Mueller, who was 26 years old, was a human rights activist and aid worker from Prescott, Ariz. She had been doing relief work with Syrian refugees in Turkey but was captured by ISIS in Aleppo, Syria."

As we've reported, Mueller was captured Aug. 4, 2013, as she left a Doctors Without Borders hospital. A family statement in February said she dedicated her career to helping people in need:

"The suffering of the Syrian refugees drew Kayla to the Turkish/Syrian border in December, 2012, to work with Support to Life, the Danish Refugee Council and other humanitarian organizations to assist families who had been forced to flee their homes. Kayla found this work heartbreaking but compelling; she was extremely devoted to the people of Syria.

"From her college graduation through 2011, she lived and worked with humanitarian aid groups in northern India, Israel and Palestine. She returned home to Arizona in 2011, and worked for one year at an HIV/AIDS clinic while volunteering at a women's shelter at night."

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