Newly released documents captured from jihadists include Islamic ruling allowing organs to be taken from captives, even if they die.

Newly released documents seized from Islamic State (ISIS) backed in May in eastern Syria by US forces include fatwa Islamic religious rulings by the group on a host of issues - including organ harvesting and rape.

The documents, seized during an operation in which ISIS chief financial officer Abu Sayyaf was killed and his wife was captured, were among seven terabytes of data picked up from computer hard drives, CDs, DVDs and papers according to Brett McGurk, the Special Presidential Envoy for the US-led coalition against ISIS.

McGurk shared several of the documents with Reuters, including religious rulings by ISIS's Research and Fatwa Committee that directly reports to ISIS leader Abu Bakr al-Baghdadi.

"Fatwa Number 64" dated from January 29, 2015, gives guidelines regarding rape, ordaining when ISIS terrorists can and cannot rape female slaves.

Another fatwa, listed as "Fatwa Number 68" from January 31, gives permission to harvest the organs of a living captive to save the life of a Muslim, even if the captive dies in the process.

"The apostate's life and organs don't have to be respected and may be taken with impunity," reads the fatwa. "Organs that end the captive's life if removed: The removal of that type is also not prohibited."

While the fatwa does not define "apostate," ISIS has murdered and tortured non-Muslims as well as Shi'ite Muslims, and even Sunni Muslims who do not follow its views.

The ruling justifies the organ harvesting by citing cannibalism it says earlier Islamic scholars allowed, saying, "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 cited Islamic texts and laws that support "the notion that transplanting healthy organs into a Muslim person’s body in order to save the latter's life or replace a damaged organ with it is permissible."

It is yet to be ascertained whether ISIS has acted on the fatwa, although Iraq has accused the jihadist group of harvesting and trafficking human organs in the past.

None of the documents had been released from the May raid until now, except for some files showing how ISIS runs a black market trade in antiquities that were made public in September at the Metropolitan Museum of Art in New York.