The cold-blooded killings allegedly took place in Mosul, the second biggest city in Iraq, after the victims were hand-picked by IS soldiers.
The women were forced into temporary marriage, or sexual jihad, and those who refused were murdered, sometimes with their families, said Kurdish Democratic Party spokesman Said Mamuzini.
“At least 250 girls have so far been executed by the IS for refusing to accept the practice of sexual jihad, and sometimes the families of the girls were also executed for rejecting to submit to IS’s request,” Mr Mamuzini told AhlulBayt news agency.
Another official, Ghayas Surchi from the Patriotic Union of Kurdistan said women were not allowed to go out alone in the city or choose their own spouse.
IS forcefully gained control of Mosul in June 2014 after the fall of the Iraqi army, but US President Barack Obama said he was positive the city would be reclaimed “eventually”.
“My expectation is that by the end of the year, we will have created the conditions whereby Mosul will eventually fall,” Mr Obama said on Monday.
The horrific executions echo similar killings that took place last August, when almost two dozen women from Mosul were slain for refusing sex with Islamic State soldiers.