The women were burned to death in iron cages because they refused to have sex with Isis fighters, the Kurdish ARA News agency reported.
“They were punished for refusing to have sex with Isis militants,” Abdullah al-Malla, a local media activist, told the agency.
An eyewitness in Mosul told ARA News: “The 19 girls were burned to death, while hundreds of people were watching."
"Nobody could do anything to save them from the brutal punishment."
Thousands of Yazidi women were taken captive when Isis seized control of Sinjar, in north western Iraq, in August 2014.
The Iraqi army is preparing for an assault on the Isis stronghold of Fallujah.
Soldiers have secured a neighbourhood to the south of the city and are poised to enter the centre of the city.
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