German prosecutors on Friday (December 28th) announced war crimes charges against a female member of the "Islamic State of Iraq and Syria" (ISIS) who let a 5-year-old girl die of thirst in the scorching sun.

While living in then ISIS-occupied Mosul, Iraq, the 27-year-old German citizen identified only as Jennifer W. and her husband had purchased the child as a household "slave" in 2015, prosecutors said.

"After the girl fell ill and wet her mattress, the husband of the accused chained her up outside as punishment and let the child die of thirst in the scorching heat," they said in a statement.

"The accused allowed her husband to do so and did nothing to save the girl."

The federal prosecutors said they had laid the charges of war crimes, murder and weapons offenses back on December 14th in a Munich court that deals with state security and terrorism cases.

Jennifer W. had first left Germany in August 2014 and travelled via Turkey and Syria to Iraq where she joined ISIS the following month.

Recruited to a vice squad of the group's self-styled morality police, she would later patrol the city parks of the ISIS-occupied cities of Fallujah and Mosul.

"Her task was to ensure that women comply with the behavioural and clothing regulations established by the terrorist organisation," said the statement.

"For intimidation, the accused carried an assault rifle of the type Kalashnikov, a pistol and an explosives vest."

Arrested in Turkey, extradited to Germany

In January 2016, months after the child's death, W. visited the German embassy in Ankara to apply for new identity papers.

When she left the mission, she was arrested by Turkish security services and extradited several days later to Germany.

For lack of actionable evidence against her, she was initially allowed to return to her home in the state of Lower Saxony.

"Since then her declared goal has been to return to the territory under ISIS rule," said the prosecutors.

When she attempted to again travel to Syria in June of this year, German police arrested her.

No date has been set yet for the start of the trial. If found guilty, she would face up to life in jail.