A man who was 16 when he told a 12-year-old girl that he would send around photos of her in a sexual act if she did not do the same with another boy, has been jailed for four years.

The man, now aged 20, had previously forced the child to perform oral sex on him while other youths recorded the act on their mobile phones.

He pleaded guilty to two counts of sexual exploitation of a child at a place in Dublin on 21 and 25 August 2015.

Passing sentence, Mr Justice Michael White said he was struck by the "cruelty" of the offences and their circumstances. He said he was concerned by the man minimising the offences while engaging with the Probation Service.

The judge said the case was aggravated by the seriousness of the offence, the victim's age at the time and the impact the offences have had on her.

He said in absence of mitigation he would have considered a sentence of eight years imprisonment.

He said the mitigating factors in the case were the man's early guilty plea, his lack of previous convictions at the time of the offences and the fact that he was still a minor when he committed the offences.

Mr Justice White sentenced the man to four years' imprisonment. He also ordered that the man would be subject to two years post release supervision, during which he would follow all directions of the Probation Service.

The Central Criminal Court previously heard evidence that the defendant knew the girl and they were chatting on Facebook.

They met up in a public park and he brought the girl over to a ditch and made her kneel down on the ground.

He manipulated her head and made her perform oral sex on him. She later told gardaí that she felt really dirty.

The court heard that a "group of young fellas" were standing nearby, took pictures of the incident, and showed her the photos.

The victim was able to see her face and the sexual act. She felt horrible and worried "she would get a name".

She met the defendant again four days later and he again forced her to perform oral sex on him before telling her that she had to do the same to a younger boy, or else he would show the pictures of the earlier incident to others.

His lawyers told Mr Justice White that his client believed the victim was 14 at the time and did not realise what he was doing was illegal.

Seamus Clarke SC, defending, said that the victim appeared to have wanted to "go out" with his client and that he was "less than gentlemanly" in his response to her.

In a letter to the court the defendant said he wished to apologise to the victim and said he and the other boy were "teenagers with little sense" at the time.

The court heard that since the attacks, the victim has had suicidal thoughts and has self harmed by cutting herself.

She was hospitalised from an overdose of tablets and said that members of the boy's family threatened her.

Last August, the younger boy was sentenced and ordered to complete 180 hours of community service.

His lawyers told Mr Justice White that he was in fear of the older boy, while the victim told gardaí she felt she had to do it.

Lawyers for the younger boy told the court that the older boy had asked her client "are you going to be gay?", meaning "was he afraid?".

Her client believed there would be adverse postings about him on social media, she said.

She said the incident was a once-off act, stage managed by the older boy.

Defence counsel Róisín Lacey said a Probation Service report noted that he had little understanding of the concept of consent, and did not realise the victim, and he himself, were both too young to consent.

She said he bitterly regretted his actions and was offering an unreserved apology to the victim.

Neither of the defendants can be named in order to protect the identity of the victim.

In her victim impact evidence, the girl told the court that before these incidents she was flourishing with confidence and had lots of hopes and dreams.

"After they abused me, it totally changed me. They took away my independence," she said, adding that fear has taken her over now.

She quit doing a lot of sporting and social activities that she had enjoyed, because of a fear of seeing the boys. She said she was threatened by members of their family.

She has had suicidal thoughts and has self harmed by cutting herself. She described being hospitalised from an overdose of tablets, which she swallowed after seeing one of the boys and becoming upset.

She said she was in such fear of bullying that she started to carry a knife with her when going out.

She said she is hoping to get on with her life and is looking forward to doing her Leaving Cert exam.