A teenage altar boy who carried out a serious indecent attack on a 12-year boy has been locked up for three years.

Christopher Beuckmann, who was 15 at the time of the incident, blocked the boy's way as he walked to a friend's home in Kilmacolm. He then pulled him to a cycle path and forced him to commit a sex act.

The victim, who Beuckmann did not know, was warned he would be punched if he did not comply. He was also told not to tell anyone what had happened because people would think he was gay.

Sixteen-year-old Beuckmann, from Bridge of Weir, earlier admitted committing the sex attack on the youngster on October 21 last year.

On Thursday, a judge told Beuckmann at the High Court in Edinburgh: "Anyone could understand that this must have been a truly horrifying experience for a young boy."

Lord Turnbull said: "There is no doubt this was a most serious offence indeed. The victim was a young boy who was deliberately selected by you on account of his age and vulnerability."

Earlier, the court heard the victim was told by Beuckmann to follow him. Advocate depute Richard Goddard said: "He found his demeanour and tone of voice intimidating and he was afraid."

When they got out of site of passers-by the teenager pulled the boy under a bridge and kissed him. The boy tried to push him away but Beuckmann put a hand over his mouth and the other around his neck. The schoolboy was forced to the ground but shouted at Beuckmann telling him to leave him alone.

Mr Goddard added: "He hoped that his shouting would attract somebody, but no one came."

The prosecutor said Beuckmann told the boy to perform a sex act, which he refused to do. He was threatened he would be punched in the face, and forced into the act. Defence counsel Laura Reilly said: "It is a very, very anxious case. It is a very disturbing case." She added that Beuchmann had "a very difficult upbringing".

She said he was an altar boy at the time of his arrest and still attended chapel in Polmont Young Offenders' Institution.