The wife of a top Islamic State (IS) leader killed in a US raid has been charged in America with contributing to the death of hostage Kayla Mueller.

A criminal complaint accuses Nisreen Assad Ibrahim Bahar, also known as Umm Sayyaf, and her husband of holding Ms Mueller, 26, captive, where officials say she was repeatedly forced to have sex with Abu Bakr al-Baghdadi, the leader of the IS group.

Umm Sayyaf is charged with conspiracy to provide material support to a foreign terror organisation, resulting in death.

The case was filed by federal prosecutors in Alexandria, Virginia, a year after aid worker Ms Mueller was confirmed dead by her family and the Obama administration, though it is not clear if or when Umm Sayyaf will be brought to the US to stand trial.

Her husband, Abu Sayyaf, a former IS minister for oil and gas, was killed last May in a Delta Force commando raid on his compound in Syria.

Iraqi Umm Sayyaf, 25, who was captured last year, is currently in custody and facing prosecution in her home country.

"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, head of the justice department's national security division, said.

"At the same time, these charges reflect that the US justice system remains a powerful tool to bring to bear against those who harm our citizens abroad. We will continue to pursue justice for Kayla and for all American victims of terrorism."

Ms Mueller, from Prescott, Arizona, was taken hostage with her boyfriend Omar Alkhani in August 2013 after leaving a Doctors Without Borders hospital in Aleppo, Syria, where Mr Alkhani had been hired to fix the internet service for the hospital.

Ms Mueller begged him to let her come along because she wanted to do relief work in the war-ravaged country. Mr Alkhani was released after two months, having been beaten.

In September 2014, Ms Mueller was transferred along with two Kurdish women of Yazidi descent from an IS prison to the Sayyafs, according to the FBI affidavit, which says the couple at times handcuffed the captives, kept them in locked rooms, dictated orders about their activities and movements, and showed them violent propaganda videos.

After her capture last year, the affidavit says, Umm Sayyaf admitted she was responsible for Ms Mueller's captivity while her husband travelled on IS business.

The Justice Department complaint echoes earlier assertions from US intelligence officials who had told Ms Mueller's family that their daughter was repeatedly forced to have sex with al-Baghdadi.