A “cold and calculated” paedophile who blackmailed Hertfordshire schoolgirls as young as 12 into sending nude photographs of themselves has been jailed.

Keelan Rowley, 20, targeted 14 girls – including four who were just 12 years old – on social media sites including Instagram and Snapchat. He was jailed for more than five years on Tuesday.

Chelmsford Crown Court heard how during 2015, predatory Rowley targeted the schoolgirls – who all lived in the Hertfordshire area – and demanded they send nude photographs or videos of themselves.

Rowley told the girls that if they refused he would subject them to sexual violence or share intimate pictures of them with their friends and family.

The court heard how two of the terrified victims complied with Rowley’s demands, and he posted images and footage of them on social media.

But Rowley, of Ruaton Drive in Clacton, soon came to the attention of Herts police – and when he was traced to his home address, the investigation was passed to Essex Police’s specialist Police Online Investigation Team, POLIT.

Officers found Rowley had targeted four 12-year-olds, two thirteen-year-olds, two girls aged 14, one girl aged 15, and three girls aged 16.

One girl refused to co-operate with police.

Rowley was subsequently charged and, on Tuesday, he pleaded guilty at Chelmsford Crown Court to a string of child sex abuse offences.

He was sentenced the same day to 64 months behind bars, put on the Sex Offenders Register for life, and made subject to a 10-year Sexual Harm Prevention Order restricting his use of the internet.

Following the sentencing, investigating officer DC Suzanne O’Neill said: “Rowley was a cold and calculated sexual predator.

“He used social media to target young girls and blackmailed and exploited them to comply with his demands. Two of them were so terrified they did everything he asked.

“However, these girls have shown nothing but bravery and courage, and have worked with us to make sure Rowley is put behind bars – where he belongs.

“We know offenders like Rowley use social media to sexually exploit young people, and that’s why we urge people to know how to keep themselves and their loved ones safe online.”

Rowley admitted two counts of inciting a child under the age of 13 to engage in sexual activity, five counts of inciting sexual exploitation of a child aged between 13 and 17, five counts of inciting a child aged between 13 and 17 to engage in sexual activity, two counts of making an indecent image of a child, and one count of distributing an indecent image of a child.