In the footage circulated online an assailant kneels on top of the teen touching and hitting her as she struggles in the dusty ground to get free.
"Don't you have a sister?" she cries out, as a third person films the assault.
Moroccan police announced that they had opened an investigation into the video to "identify the attacker" and "determine where and when this crime took place." Local media outlets called the incident "a scene of rare violence" and "atrocious".
Morocco publisher accused of 'sexual assault'
Women are frequently subjected to insults, derogatory remarks and other sexist attacks in public.
Last month, after years of debate, the country passed a law to combat violence against women that officials said criminalises "acts considered forms of harassment, aggression, sexual exploitation or ill treatment".
Women's organisations said the law passed did not go far enough. In a society divided between conservative and progressive strands, violence against women, especially in public, is often highlighted in the media and by rights groups.
Police arrest pair over rape of mentally-challenged woman in India
It became a hot issue last August after a video was posted on the internet showing a young woman on a bus being sexually molested by a group of boys without the driver or other passengers reacting to her appeals for help.
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