There is growing evidence that extremist groups including the Islamic State and Boko Haram are reviving slavery and organizing slave markets, according to a report launched Thursday. James Cockayne, head of the United Nations University office in New York and lead author of the report, said ''we're seeing horrifying new twists'' on the ancient problem of human trafficking in conflict. Social media apps and websites have made it possible to engage and recruit potential human trafficking victims, and trade them ''in a way that wasn't possible before,'' he said. Islamic State extremists, for example, ''have published a `How To' manual'' that says enslavement is legally justified in some cases, despite international law banning all slavery, Cockayne said. According to the report, Islamic State militants in Iraq are thought to have enslaved over 5,000 women, children and men from the Yazidi religious minority in Iraq. ''There is strong evidence that social media is being used to both recruit and trade enslaved Yazidi and other peoples,'' Cockayne said. In the past year, the report said, IS fighters have used encrypted communications app Telegram and others including WhatsApp, Twitter and Threema to auction enslaved Yazidi women and launder the profits. ''The reported numbers are small but the suspicion is a lot is going unreported in part because some of these apps are highly encrypted,'' Cockayne told the Associated Press. WhatsApp was recently used in a case of trading displaced Syrian women in Lebanon, he said. And an Islamic State member recently tried to trade enslaved women, but the information and offer were taken down by the website within hours. ''There is clearly more that the technology sector could do if they were given appropriate regulatory guidance by member states, and clearly the Security Council has a potential role here,'' Cockayne said. The report proposes ideas for action by the council, including implementation of sanctions against human trafficking and strengthening international denunciation of slavery, as well as stepped up efforts to tackle the financing, technology and recruitment that is spurring trafficking. Britain's U.N. Ambassador Matthew Rycroft said that ''with an estimated 45.8 million slaves alive today, modern slavery is one of the most significant human rights tragedies of our time'' - and conflict makes people especially vulnerable to enslavement. Liechtenstein's U.N. Ambassador Christian Wenaweser said human trafficking is also ''one of the big illegal business models that exist in the world - (and) this is something that we believe certainly needs to be addressed and has a very, very direct link on conflict situations.'' In certain instances, he said, this can amount ''to crimes against humanity'' that could be referred to the International Criminal Court. And he said options are actively being explored with the ICC prosecutor. Both Britain and Liechtenstein supported preparation of the report, which is expected to provide ideas to Security Council members who will debate the issue of human trafficking in conflict in December.