SINGAPORE - An 18-year-old youth was at home with his younger sister in April this year when he repeatedly asked her to sexually stimulate him, promising to buy her merchandise of Korean pop group BTS in return.

The 12-year-old girl rejected his requests and told the police later that month.

The offender, who cannot be named owing to a court order to protect the girl's identity, also molested her on two separate occasions.

He pleaded guilty on Tuesday (Dec 3) to asking his sister to perform an obscene act on him.

He also admitted to two counts of outraging her modesty in January and February this year.

In the January incident, the girl had gone into her brother's room and sat on his bed. She bolted from the room when he suddenly rubbed her private parts with his hand, the court heard.

Their family moved to another home soon after and the pair shared the same bedroom.

The teenager and his sister were in the living room in mid-February when they started arguing over what to watch on television.

Deputy Public Prosecutor Ryan Lim told District Judge Seah Chi-Ling: "The accused suddenly picked the victim up, carried the victim to their bedroom... and laid her on his bed.

"(The) accused used the fingers of his left hand to stroke the side of the victim's right breast over the victim's T-shirt in an upwards and downwards motion. The touching was non-fleeting."

The girl yelled at her brother to get out of the bedroom and he complied, the court heard.

DPP Lim said that on April 15, the girl came home around 6pm and found the door to their bedroom was closed.

She knocked and when there was no response, she opened it and saw her brother performing a sexual act.

She closed the door and went to the living room. He came out and asked her to sexually stimulate him. She made a police report nine days later.

Judge Seah has called for a report to assess the teenager's suitability for probation and reformative training.

Offenders given reformative training will be detained in such a centre where they will follow a strict regimen that includes foot drills and counselling.

The teenager will be sentenced on Dec 10.

For each count of molestation involving a victim below age 14, an offender can be jailed for up to five years and fined or caned.