Islamic State militants have executed five members of an Iraqi family because the parents refused to allow their daughter to marry a fighter in the group, according to Iraqi officials.

After killing the family members, Islamic State militants kidnapped the 14-year-old girl and took her to an unknown location, according to a statement from Iraq's Human Rights Ministry, which called the murders a "horrific crime."

Islamic State militants killed the mother, father, and three children before kidnapping the daughter, officials said. The Human Rights Ministry said in the statement that the Islamic State fighter who was trying to marry the girl was Saddam al-Jamal.

The statement did not disclose when and where the murders took place.

Jamal is a former drug dealer who was a commander in the Free Syrian Army before he defected to the Islamic State. It's not clear if Jamal is directly responsible for the murder of the Iraqi family, but a former bodyguard has disclosed previous violent acts he has committed.

Video shows Saddam al-Jamal announcing his defection to the Islamic State.

According to the bodyguard, Jamal once forced a mother and father to watch as another militant killed their children one-by-one.

"Starting with a 13-year-old boy, they lined up the sons according to their height and beheaded them in that order," the bodyguard told the International Business Times. "Afterwards, they hung the boys' heads on the door of the school the family had been hiding in."

Violence has been a constant for the expanding Islamic State as it has seized large swaths of territory in Iraq and Syria over the last several months. The militant group has posted videos showing the beheadings of captive American and British journalists, which have prompted a strong international reaction and instigated a US-led coalition to launch airstrikes on the group in both Iraq and Syria, which have had varying degrees of success.

The Islamic State's media arm posted a video on Sunday that revealed the group had beheaded captive American aid worker Peter Kassig, along with several Syrian soldiers. The White House confirmed the authenticity of the video after reviewing the clip, according to a report from USA Today.