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An Islamic State militant who helped imprison and brutalize American hostage Kayla Mueller will not be charged in the U.S., the White House announced Friday.

WASHINGTON — An Islamic State militant who helped imprison and brutalize American hostage Kayla Mueller will not be charged in the U.S., the White House announced Friday.

The militant known as Umm Sayyaf, who had been cooperating with American military interrogators after she was captured in Syria during a May U.S. Special Operations raid, will be prosecuted in the Kurdish region of Iraq by Kurdish authorities, White House spokesman Josh Earnest said.

She will be tried in the Kurdish system. "While we obviously can't guarantee a particular result, we do have a firm belief that she will be held accountable for her crimes," Earnest said.

On Thursday, the Defense Department announced that Umm Sayyaf has been transferred to a facility in the Iraqi Kurdish capital of Irbil. She is the wife of an Islamic State financier known as Abu Sayyaf, who was killed during the Delta Force raid.

Another senior Islamic State figure took Mueller as a "wife," and visited her occasionally while she lived with the Sayyaf couple, according to two American officials who spoke on condition of anonymity because the details are classified. They declined to name the Islamic State official.

Documents seized at the site, and hours of conversations with Umm Sayyaf, have provided American officials with some of their best intelligence to date on the Islamic State, U.S. officials have said.

Mueller, who was from Prescott, Arizona, and her Syrian boyfriend were taken hostage in August 2013 after leaving a Doctors Without Borders hospital in Aleppo, Syria. The boyfriend was later released. In February, the Islamic State announced her death, saying she had been killed in a Jordanian air strike. U.S. officials have never confirmed that.

Earnest said Umm Sayyaf "will be held accountable for her crimes," in Iraq.

Associated Press writer Connie Cass contributed to this report.