A female member of the Islamic State jihadist group let a five-year-old girl die of thirst in the scorching sun, according to German prosecutors.

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

"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 offences back on December 14 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 the IS the following month.

Recruited to a vice squad of the militant group's self-styled morality police, she would later patrol the city parks of the IS-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.