Isil tortured and abused 150 Kurdish boys in Syria a human rights group has revealed.
The traumatised captured children described being beaten with cables while held captive by the jihadi group in the beseiged Syrian town of Kobane.
Isil militants have taken hundreds of Kurds captive over the past year as part of the group's brutal campaign to take over predominantly Kurdish areas.
According to the new report Isil forced children as young as 14 to watch videos of beheadings and then beat them with cables during six months of captivity, Human Rights Watch revealed yesterday.
The Sunni Muslim militants abducted a group of children on May 29 as they returned to Kobane after taking school exams in the city of Aleppo. It freed the final 25 hostages at the end of last month.
The abuse of more than 150 children, some held as long as six months, amounted to war crimes, Human Rights Watch said, citing testimony from four boys among the group.
The children described being forced to pray five times a day and undergoing intense religious instruction, as well as being forced to watch videos of Islamic State in combat and beheading captives, the New York-based group said.
"Those who didn't conform to the programme were beaten. They beat us with a green hose or a thick cable with wire running through it. They also beat the soles of our feet," it quoted one boy as saying.
"They sometimes found excuses to beat us for no reason... They made us learn verses of the Koran and beat those who didn't manage to learn them."
The boys said they were given no reason for their release other than that their religious education was now over.
The last children to be released by Isil were now seeking shelter in Turkey, the rights group said.
Those from families with members fighting with the Kurdish militia, called YPG, which has been defending Kobane, were singled out for special abuse, the children said.
Their captors - who came from Syria, Jordan, Libya, Tunisia and Saudi Arabia - "told them to give them the addresses of their families, cousins, uncles, saying, 'When we go to Kobane, we will get them and cut them up.' They saw the YPG as infidels," one 15-year-old boy said in his evidence.
Other Kurdish children and adults are still in captivity, the children said. Isil is also thought to hold less than 10 Western hostages, including foreign journalists.
The United States and its allies have pounded Isil targets in Iraq and Syria since August, stepping up the bombardment after the insurgents moved in on Kobane in October.
Isil has captured swathes of Iraq and Syria, declaring an Islamic caliphate that erases borders between the two. Its fighters have killed or driven away Shia Muslims, Christians and other communities who do not share their ultra-radical brand of Sunni Islam.
Kobane - a predominantly Kurdish town on the Syrian border with Turkey - has been besieged by Islamic State militants for more than a month, despite US-led air strikes meant to displace them.
Meanwhile, a warning has been issues that extremists of all kinds are relying on social media to recruit, radicalise and raise funds.
Robert Hannigan - the new head of GCHQ, the British intelligence service - spelled out how Isil terrorists in Syria and Iraq have "embraced the web".
He also claimed that terrorists were now able to hide their identities using encryption tools which were once only available to government agencies.
Isil has proved fluent in YouTube, Twitter, Instagram, Tumblr, internet memes and other social media. Its posting activity has ramped up during a recent offensive, reaching an all-time high of almost 40,000 tweets in one day as they marched into the northern Iraqi city of Mosul. (© Daily Telegraph, London)