ISIS has sanctioned the harvesting of human organs in a previously undisclosed ruling by the group’s Islamic scholars, raising concerns that the violent extremist group may be trafficking in body parts.

The ruling, contained in a January 31, 2015, document, says taking organs from a living captive to save a Muslim's life, even if it is fatal for the captive, is permissible.

"The apostate's life and organs don't have to be respected and may be taken with impunity," says the document, which is in the form of a fatwa, or religious ruling, from ISIS' Research and Fatwa Committee.

"Organs that end the captive's life if removed: The removal of that type is also not prohibited," Fatwa Number 68 says, according to a U.S. government translation. 

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The document does not offer any proof that ISIS actually engages in organ harvesting or organ trafficking. But it does provide religious sanction for doing so under the group's harsh interpretation of Islam – which is rejected by most Muslims. Previously, Iraq has accused ISIS of harvesting human organs and trafficking in them for profit.

The document does not define “apostate,” though ISIS has killed or imprisoned non-Muslims, such as Christians, and Shiite Muslims, as well as Sunni Muslims, who don't follow its extremist views.

U.S. officials say the records that were seized have given the U.S. government a deep look into how ISIS organizes, raises funds and codifies laws for its followers.

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The group of documents – entitled "Lessons Learned From the Abu Sayyaf Raid" – shows how ISIS has provided a legal justification to its followers for a range of practices. 

For instance, “Fatwa Number 64,” dated January 29, 2015, provides detailed rules for rape, prescribing when ISIS men can and cannot have sexual intercourse with female slaves.

The fatwa sanctioning organ harvesting justifies the practice in part by drawing an analogy to cannibalism in extreme circumstances, a practice it says earlier Islamic scholars had allowed. “A group of Islamic scholars have permitted, if necessary, one to kill the apostate in order to eat his flesh, which is part of benefiting from his body,” it says.

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William McCants, a Brookings Institution scholar who is author of the book “The ISIS Apocalypse,” said the group's ruling on slavery and human organs doesn't represent modern Islamic interpretations.

The U.N. special envoy for Iraq, Nickolay Mladenov, said that he could not confirm the claim, but it would be investigated. The U.N. has not provided an update on that investigation.