A document found by the US in a raid in Syria in May has revealed a ruling issued by the Islamic State's Research and Fatwa Committee permitting organ harvesting from "apostates".

The document from 31 January, 2015, says ending an apostate's life for the purpose of transplanting organs is legal. It says: "Transplanting healthy organs from an apostate's body into a Muslim body in order to save the latter's life or replace a damaged organ with it is permissible.

"The apostate's life and organs don't have to be respected and may be taken with impunity," adds the document.

Quoting religious texts and principles, the ruling argues if Islamic scholars had permitted cannibalism to keep a Muslim alive, organ harvesting is legal too.

The harvesting can be done pre and post-mortem, says the translated document acquired by Reuters.

The fatwa was discovered among a trove of other such documents by the US during a raid in May in Syria. The raid had killed top Isis financial official Abu Sayyaf and captured his wife, which led to the confiscation of many terabytes of information.

Reuters quoted Iraq's ambassador to the UN Mohamed Ali Alhakim as saying that the UN Security Council needs to examine the documents to find out if Daesh is harvesting organs for money.

He also alleged that 12 doctors were killed in Mosul for refusing to perform organ transplant.

Alhakim also told Reuters he would ask the UN to look into the issue of organ harvesting by Islamic State again. UN reported no updates regarding the investigation.

Another fatwa found in the raid enlists the reasons that justify rape of female slaves, reports Reuters.