The Islamic State group, also known as ISIS, has executed at least 250 women in northern Iraqi city of Mosul in Nineveh province for refusing sex slavery, according to reports Wednesday. The women had been ordered to accept “temporary marriages” to the militants, and were all put to death after their refusal.

Said Mamuzini, an official from the Kurdistan Democratic Party, told the AhlulBayt News Agency that sometimes the families of the women were also executed for rejecting to submit. Ghayas Surchi, another official, from the Patriotic Union of Kurdistan, told the news agency that women are not allowed to go out alone in Mosul and are required to be completely covered in public. Surchi said that women are also barred from choosing their spouses.

Mosul, the ISIS stronghold, has been under ISIS rule since June 2014.

Earlier this year, it was reported that several teachers and civil servants in Mosul were executed by the ISIS for refusing to follow a new curriculum the militants had introduced to schools. The militants also raided schools and arrested dozens of teachers from Nineveh province for refusing to teach their students the new curriculum. ISIS reportedly removed major subjects, including math, biology, chemistry and philosophy, from school curriculums across Syria and Iraq and replaced them with lessons on jihad and the history of ISIS.

“These essential courses have been replaced by some extremist subjects on so-called Shariah and jihad, designed by the group to ideologize students and gain their support to the alleged caliphate,” a teacher said told AhlulBayt at the time.

The Iraqi army has begun preparatory operations in Nineveh against the militants. However, the actual assault to retake Mosul is expected to take place possibly not until next year.

On Monday, United States President Barack Obama said that he expects Mosul to be retaken from ISIS “eventually.”

“As we see the Iraqis willing to fight and gaining ground, let's make sure that we're providing them more support,” Obama said, in an interview to CBS News, according to Agence France-Presse. “We're not doing the fighting ourselves, but when we provide training, when we provide special forces who are backing them up, when we are gaining intelligence -- working with the coalitions that we have -- what we've seen is that we can continually tighten the noose,” he added.

“My expectation is that by the end of the year, we will have created the conditions whereby Mosul will eventually fall.”