WASHINGTON - Islamic State ‘theologians’ have issued an extremely detailed ruling on when “owners” of women enslaved by the extremist group can have relations with them, in an apparent bid to curb what they called 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 the subject, a leading Islamic State ‘scholar’ said. 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. Reuters has reviewed the document, which has not been previously published, but couldn’t independently confirm its authenticity.

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. Joint owners of a female captive are similarly enjoined from having relations because she is viewed as “part of a joint ownership.” The UN 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.

In an April report, Human Rights Watch interviewed 20 female escapees who recounted how Islamic State fighters separated young women and girls from men and boys and older women. They were moved “in an organized and methodical fashion to various places in Iraq and Syria.” They were then sold or given as gifts and repeatedly raped or subjected to sexual violence. ‘fatwa’ No. 64, dated Jan. 29, 2015, and issued by Islamic State’s Committee of Research and ‘fatwa’s, appears to codify sexual relations between IS fighters and their female captives for the first time, going further than a pamphlet issued by the group in 2014 on how to treat slaves.

The ‘fatwa’ starts with a question: “Some of the brothers have committed violations in the matter of the treatment of the female slaves. These violations are not permitted by Sharia law because these rules have not been dealt with in ages. Are there any warnings pertaining to this matter?”

It then lists 15 injunctions, which in some instances go into explicit detail. For example: “If the owner of a female captive, who has a daughter suitable for relations, has sexual relations with the latter, he is not permitted to have sex with her mother and she is permanently off limits to him. Should he have sex with her mother then he is not permitted to have sex with her daughter and she is to be off limits to him.”

Islamic State’s rape of female captives has been well documented, but a leading IS expert at Princeton University, Cole Bunzel, who has reviewed many of the group’s writings, said the ‘fatwa’ went beyond what has previously been published by the militants on how to treat female slaves. “It reveals the actual concerns of IS slave owners,” he said in an email.

Still, he cautioned that not “everything dealt with in the ‘fatwa’ is indicative of a relevant violation. It doesn’t mean father and son were necessarily sharing a girl. They’re at least being ‘warned’ not to. But I bet some of these violations were being committed.”

The ‘fatwa’ also instructs owners of female slaves to “show compassion towards her, be kind to her, not humiliate her, and not assign her work she is unable to perform.” An owner should also not sell her to an individual whom he knows will mistreat her.

Professor Abdel Fattah Alawari, dean of Islamic Theology at Al-Azhar University, a 1,000-year-old Egyptian center for Islamic learning, said Islamic State “has nothing to do with Islam” and was deliberately misreading verses and sayings that were originally designed to end, rather than encourage, slavery.

“Islam preaches freedom to slaves, not slavery. Slavery was the status quo when Islam came around,” he said. “Judaism, Christianity, Greek, Roman, and Persian civilizations all practiced it and took the females of their enemies as sex slaves. So Islam found this abhorrent practice and worked to gradually remove it.”

In September 2014 more than 120 Islamic scholars from around the world issued an open letter to IS leader Abu Bakr al-Baghdadi refuting the group’s religious arguments to justify many of its actions. The scholars noted that the “reintroduction of slavery is forbidden in Islam.”

Meanwhile, a US-led coalition has killed 10 Islamic State leaders in the past month with targeted air strikes, including individuals linked to last month’s attacks in Paris, a spokesman for the coalition said on Tuesday.

“Over the past month, we’ve killed 10 ISIL leadership figures with targeted air strikes, including several external attack planners, some of whom are linked to the Paris attacks,” said US Army Colonel Steve Warren, a spokesman for the US-led military campaign against Islamic State, also known by the acronym ISIL. “Others had designs on further attacking the West.”

One of those killed was Abdul Qader Hakim, who facilitated the militants’ external operations and had links to the Paris attack network, Warren said. He was killed in the northern Iraqi city of Mosul on Dec. 26.

Iraqi Prime Minister Haider al-Abadi planted the national flag in Ramadi on Tuesday after the army retook the city centre from Islamic State a day earlier, a victory that could help vindicate his strategy for rebuilding the military after stunning defeats.

If the Anbar provincial capital can be fully secured and re-populated, it would be the first major success for the US-trained force that fled 18 months ago as jihadist Islamic State militants surged through northern and western Iraq.

Security forces must still remove explosives planted in streets and buildings and clear out fighters in some densely built-up areas, and much of the infrastructure needs to be rebuilt.

Three mortar rounds landed about 500 meters (0.3 miles) from Abadi’s location during his visit, three security sources said. The prime minister was not in danger but was forced to leave the area, they said.

Abadi had arrived in Ramadi by helicopter. He moved through the city with the Anbar governor and top security officials in a convoy of Humvees, crossing a floating bridge used by the armed forces last week to retake the city centre.

He met soldiers at the main government complex captured by counter-terrorism forces on Monday and planted the tri-colour flag outside the building.