ISLAMIC State theologians have issued an extremely detailed ruling on when “owners” of women enslaved by the extremist group can have sex with them, in an apparent bid to curb what they call violations in the treatment of captured females.

The ruling, or fatwa, has the force of law and appears to go beyond the Islamic State’s previous known utterances on slavery, said Cole Bunzel, a leading IS expert at Princeton University.

It sheds new light on how the group is trying to reinterpret centuries-old teachings to justify the rape of women in the swathes of Syria and Iraq it controls.

MORE: Islamic State’s “war spoils” department

The fatwa was among a huge trove of documents captured by US Special Operations Forces during a raid targeting a top Islamic State official in Syria in May.

Among the fatwa’s injunctions are bans on a father and son having sex with the same female slave and the owner of a mother and daughter having sex with both. There are also rules around pregnancy, “joint ownership” and abortions.

ISLAMIC STATE’S NEW RULES

• “It is not permissable for the owner of a female captive to have intercourse with her until after she has her menstrual cycle and becomes clean.”

• “If she is pregnant, he is not allowed to have intercourse with her until after she has given birth.”

• “It is not permissable to cause her to abort if she is pregnant.”

• “If the owner of a female captive releases her, only he can have intercourse with her and he cannot allow someone else to have intercourse with her.”

• “If the owner of a female captive, who has a daughter suitable for intercourse, has sexual relations with the latter, he is not permitted to have intercourse with the mother and she is permanently off-limits to him.”

• “The owner of two sisters is not allowed to have intercourse with both of them.”

• “If the female captive becomes pregnant by her owner, he cannot sell her and she is released after his death.”

• “If two or more individuals are involved in purchasing a female captive, none of them are permitted to have intercourse with her because she is part of a joint ownership.”

The US government’s full translation of the list, which has not been previously published, is here. It makes for grim reading.

Twelve months ago, IS released a similarly sickening list of 27 tips for raping and punishing sex slaves. Those guidelines were set out as a Q&A explainer on how to capture and degrade young women and pre-pubescent girls, which tried to justify such behaviour through Islamic law.

The pamphlet, published by the IS “Research and Fatwa Department”, insisted it was acceptable to have sexual intercourse with non-Muslim slaves, including young girls, and said militants were also permitted to beat and trade them.

“There is no dispute among the scholars that it is permissable to capture unbelieving women,” the pamphlet said.

“It is permissable to buy, sell or give as a gift female captives and slaves, for they are merely property.

“It is permissable to have intercourse with a female slave who hasn’t reached puberty if she is fit for intercourse.”

A translation of that list is also available online. You can find it here.

The United Nations and human rights groups have accused the Islamic State of the systematic abduction and rape of thousands of women and girls as young as 12, especially members of the Yazidi minority in northern Iraq.

Many have been given to fighters as a reward or sold as sex slaves. Far from trying to conceal the practice, Islamic State has boasted about it and established a department of “war spoils” to manage slavery.

The terrorist collective’s complex system of departments was described in the same cache of documents that included the new rules for sex slaves.

US officials say the documents have helped deepen their understanding of a militant group whose skill in controlling the territory it has seized has surprised many. They provide insight into how a once small insurgent group has developed a complex bureaucracy to manage revenue streams — from pillaged oil to stolen antiquities — and oversee subjugated populations.

“This really kind of brings it out. The level of bureaucratization, organisation, the diwans, the committees,” Brett McGurk, President Barack Obama’s special envoy for the anti-ISIS coalition, told Reuters.

For example, one diwan, roughly equivalent to a government ministry, handles natural resources, including the exploitation of antiquities from ancient empires. Another processes “war spoils,” including slaves.