A 25-year-old salesman, who was the leader of a youth gang when he repeatedly raped a girl when she was 13, was sentenced to 28 years' jail and 24 strokes of the cane yesterday.

The High Court said a stiff sentence was warranted to reflect his culpability and to deter him and others from committing such offences.

"There were clear aggravating factors and, in my view, no mitigating circumstances," said Judicial Commissioner Audrey Lim.

Koh Rong Guang, who is also known as Charles, is appealing and was granted bail, which was increased from $80,000 to $100,000.

Koh had claimed trial to 12 charges - four of statutory rape, one of sexual assault by penetration, three of criminal intimidation, two of committing an indecent act with a young person, one of causing hurt, and one of circulating a nude photo of the girl.

The rapes took place at the staircase of a karaoke outlet in Choa Chu Kang Centre and the staircase of a block of flats in Choa Chu Kang Crescent, near the Yew Tee Foodfare coffee shop.

During his trial, Koh denied the charges, insisting that he had never touched the girl, who is now 17. He contended that she had made up the allegations to get back at him for posting photos of her in sexually explicit poses with his "best bro" in the gang, Fu Yiming. Koh had met the girl through Fu.

In one incident, Koh used a spanner to hit the wall close to the victim's face before sexually assaulting her. In the last incident, he punched and kicked Fu, who had accompanied the victim to meet him, and threatened them with a brick.

Last month, the court found him guilty of 11 charges. Koh was acquitted of the first rape charge as the court found there was no corroboration of the victim's account.

Yesterday, it emerged in court that Koh was on probation for rioting with a deadly weapon when he committed the offences between November 2013 and January 2014.

"Despite being given the opportunity at rehabilitation, the accused had failed to turn over a new leaf. Instead, he graduated to more heinous crimes," said Deputy Public Prosecutor David Khoo.

The prosecutor argued that Koh treated the victim as someone to have sex with and then discard once he was done toying with her.

He said Koh's carefully planned offences were carried out against a vulnerable child "who faced significant barriers to seeking help amid the cycle of abuse she was entangled in".

DPP Khoo said the girl was already being abused by her father, and Koh's offences added to the psychological damage she suffered.

She resorted to self-harm to cope with Koh's persistent sexual assault and the scars remain on her arms, said the DPP.

The prosecutor argued that Koh not only raped her and made her strip to take nude photos of her, but also offered her to his friends as if she was his property.

In a separate incident, one of the teens in the gang, Alson Tan Yu Seng, 15, went on to rape the girl while two of his friends pinned her down.

Tan told his friends - Bryan Ong Jing Chong and Tan Wei Guang - he had seen his headman rape the girl and suggested that they have sex with her. The trio played a game of scissors-paper-stone to decide who would go first. But the two friends did not go on to rape the girl as the trio were interrupted. They were charged with abetting Alson Tan.

All three were sentenced to reformative training.