Handcuffs (illustrative)
Handcuffs (illustrative)Thinkstock

The widow of late ISIS financial leader Abu Sayyaf was charged Monday for her alleged role in the death of US aid worker Kayla Mueller last year.

Nisreen Assad Ibrahim Bahar, a 25-year-old known as Umm Sayyaf, was accused of conspiring to provide support to the violent extremists, forcibly detaining Mueller and other captives in the couple's homes, where she was sexually assaulted by ISIS chief Abu Bakr al-Baghdadi.

Bahar acknowledged that Baghdadi "owned" Mueller during her captivity at the Sayyaf residences, describing "owning" as equivalent to slavery, federal prosecutors said.

ISIS fighters claimed that Mueller, who was kidnapped in the Syrian city of Aleppo in August 2013, was killed in a February 2015 coalition air strike that buried her in rubble.

US officials say the circumstances of her death remain unclear. She was 26.

Abu Sayyaf was killed in May 2015 in a rare US commando raid inside war-torn Syria.

Bahar was captured during the operation, and US forces also rescued a young woman from the Yazidi minority and seized a stash of firearms, the complaint recalled.

Mueller and other female "captives were at various times handcuffed, held in locked rooms and given orders on a daily basis with respect to their activities, movements and liberty," according to a complaint filed in US District Court in Virginia.

"While in captivity, Kayla Jean Mueller was sexually abused by Baghdadi, who forced her to have sex with him," it added.

"The defendant (Bahar) knew how Ms. Mueller was treated by Baghdadi when Ms. Mueller was held against her will in the defendant's home."

The complaint also alleged that Bahar told the captives that "she would kill them if they did not listen to her."

Bahar admitted that she had sole responsibility for holding the hostages captive while her husband traveled on ISIS business, and that Baghdadi and other members of the group would stay at the residence at times, according to the complaint.

If convicted, Bahar faces life in prison. She is currently in Iraqi custody, facing prosecution for terror-related activities.

"We fully support the Iraqi prosecution of Sayyaf and will continue to work with the authorities there to pursue our shared goal of holding Sayyaf accountable for her crimes," Assistant Attorney General John Carlin said in a statement.

"We will continue to pursue justice for Kayla and for all American victims of terrorism."

AFP contributed to this report