Before you go, we thought you'd like these...  As the operation to retake the city of Mosul from ISIS ramps up, anti-ISIS forces are detailing some of the atrocities committed by the terrorist group.  SEE ALSO: Saudi snub? Royal family skips Obama's arrival  An official for the Kurdistan Democratic Party told Iranian news agency ABNA ISIS has been forcing women into arranged marriages with ISIS fighters — and executing women who refuse.  The official said "at least 250 girls have so far been executed ... and sometimes the families of the girls were also executed."  See images from clashes between Kurdish forces and ISIS:  Kurdish official says ISIS executed 250 women in Mosul  SANLIURFA, TURKEY - JUNE 25: People gather at the borderline between Turkey and Syria in Sanliurfa province on June 25, 2015 as smoke rises from the Syrian border town of Kobani (Ayn al-Arab) during the clashes between Daesh militants and and Kurdish armed groups. (Photo by Halil Fidan/Anadolu Agency/Getty Images)  SANLIURFA, TURKEY - JUNE 25 : A picture taken from Suruc district of Turkey's Sanliurfa province shows people seen at Turkish border as smoke trails over during the clashes between Daesh (Islamic State of Iraq and the Levant) terrorists and Kurdish armed groups were getting intense in the Syrian border town of Kobani (Ayn al-Arab), on June 25, 2015 in Sanliurfa, Turkey. (Photo by Halil Fidan/Anadolu Agency/Getty Images)  SANLIURFA, TURKEY - JUNE 25 : A picture taken from Suruc district of Turkey's Sanliurfa province shows a group of Syrians wait at Syrian side of Turkish border during the clashes between Daesh (Islamic State of Iraq and the Levant) terrorists and Kurdish armed groups were getting intense in the Syrian border town of Kobani (Ayn al-Arab), on June 25, 2015 in Sanliurfa, Turkey. (Photo by Halil Fidan/Anadolu Agency/Getty Images)  SANLIURFA, TURKEY - JUNE 25 : A picture taken from Suruc district of Turkey's Sanliurfa province shows a group of Syrians wait at Syrian side of Turkish border during the clashes between Daesh (Islamic State of Iraq and the Levant) terrorists and Kurdish armed groups were getting intense in the Syrian border town of Kobani (Ayn al-Arab), on June 25, 2015 in Sanliurfa, Turkey. (Photo by Halil Fidan/Anadolu Agency/Getty Images)  SANLIURFA, TURKEY - JUNE 25 : A picture taken from Suruc district of Turkey's Sanliurfa province shows a group of Syrians wait at Syrian side of Turkish border during the clashes between Daesh (Islamic State of Iraq and the Levant) terrorists and Kurdish armed groups were getting intense in the Syrian border town of Kobani (Ayn al-Arab), on June 25, 2015 in Sanliurfa, Turkey. (Photo by Halil Fidan/Anadolu Agency/Getty Images)  SANLIURFA, TURKEY - JUNE 25 : A picture taken from Suruc district of Turkey's Sanliurfa province shows a group of Syrians wait at Syrian side of Turkish border during the clashes between Daesh (Islamic State of Iraq and the Levant) terrorists and Kurdish armed groups were getting intense in the Syrian border town of Kobani (Ayn al-Arab), on June 25, 2015 in Sanliurfa, Turkey. (Photo by Halil Fidan/Anadolu Agency/Getty Images)  SANLIURFA, TURKEY - JUNE 25 : A picture taken from Suruc district of Turkey's Sanliurfa province shows a man watches developments with a binoculars as a group of Syrians wait at Syrian side of Turkish border during the clashes between Daesh (Islamic State of Iraq and the Levant) terrorists and Kurdish armed groups were getting intense in the Syrian border town of Kobani (Ayn al-Arab), on June 25, 2015 in Sanliurfa, Turkey. (Photo by Halil Fidan/Anadolu Agency/Getty Images)  SANLIURFA, TURKEY - JUNE 25 : A picture taken from Suruc district of Turkey's Sanliurfa province shows a group of Syrian wait at Syrian side of Turkish border during the clashes between Daesh (Islamic State of Iraq and the Levant) terrorists and Kurdish armed groups were getting intense in the Syrian border town of Kobani (Ayn al-Arab), on June 25, 2015 in Sanliurfa, Turkey. (Photo by Halil Fidan/Anadolu Agency/Getty Images)  SANLIURFA, TURKEY - JUNE 25 : A Syrian is being hospitalized as soon as he was received from Mursitpinar border crossing at Turkey's Syria border after he was wounded by an explosion during the clashes between Daesh (Islamic State of Iraq and the Levant) terrorists and Kurdish armed groups in the Syrian border town of Kobani (Ayn al-Arab), on June 25, 2015 in Sanliurfa, Turkey. (Photo by Rauf Maltas/Anadolu Agency/Getty Images)  SANLIURFA, TURKEY - JUNE 25 : A picture taken from Suruc district of Turkey's Sanliurfa province shows a group of Syrians wait at Syrian side of Turkish border during the clashes between Daesh (Islamic State of Iraq and the Levant) terrorists and Kurdish armed groups were getting intense in the Syrian border town of Kobani (Ayn al-Arab), on June 25, 2015 in Sanliurfa, Turkey. (Photo by Halil Fidan/Anadolu Agency/Getty Images)  SANLIURFA, TURKEY - JUNE 25 : A Syrian is being hospitalized as soon as she was received from Mursitpinar border crossing at Turkey's Syria border after she was wounded by an explosion during the clashes between Daesh (Islamic State of Iraq and the Levant) terrorists and Kurdish armed groups in the Syrian border town of Kobani (Ayn al-Arab), on June 25, 2015 in Sanliurfa, Turkey. (Photo by Rauf Maltas/Anadolu Agency/Getty Images)  SANLIURFA, TURKEY - JUNE 25 : A Syrian is being hospitalized as soon as he was received from Mursitpinar border crossing at Turkey's Syria border after he was wounded by an explosion during the clashes between Daesh (Islamic State of Iraq and the Levant) terrorists and Kurdish armed groups in the Syrian border town of Kobani (Ayn al-Arab), on June 25, 2015 in Sanliurfa, Turkey. (Photo by Rauf Maltas/Anadolu Agency/Getty Images)  Iraqi security forces display a flag of the Islamic State group and weapons and ammunition confiscated after regaining control of during operations over the last week, from towns of al-Karma and Saqlawiyah near Fallujah, at al-Taji Camp north of Baghdad, Iraq, Friday, July 10, 2015. (AP Photo/ Karim Kadim)  Mosul fell to ISIS in the summer of 2014. Since then, the group has been taking pains to portray their occupation of the city as benevolent. But ISIS' reign has been particularly oppressive to women; the group practices sex slavery and requires women to adhere to a strict set of rules.  The push to retake Mosul began last month, and President Obama says he expects the city to be ripe for the retaking by the end of the year. ​  More from AOL.com: US to send more troops to Iraq, escalating war on ISIS Vladimir Putin's annual call-in show: Russians submit 3M questions The ISIS files: What leaked documents reveal about terror recruits
The terrorist group has been accused of pressing Mosul women into forced marriages, and executing those who refuse.