A 22-year-old man with intellectually disability yesterday pleaded guilty in the High Court to a charge of attempted rape - he tried to have sex with his step-niece, then aged four, in 2012.

The man, who cannot be named under a court order, was 18 years old at the time of the offence.

The court heard that he lived with his stepfather in a two-room HDB flat after his mother remarried in July 2011.

In January 2012, the stepfather's daughter and her daughter - the victim - moved into the flat as well. The girl's mother treated the man like a brother and the girl called him "uncle", the court heard.

One evening in mid-February 2012, the man and the girl were watching TV in the living room while the girl's mother and a friend were in the kitchen.

The girl, who wanted to play with him, sat on him while they were on a mattress. He became aroused and tried to have sex with the girl, but did not succeed.

The girl then pulled up her shorts and underwear and ran to the kitchen, crying and telling her mother that her uncle tried to "kacau" ("disturb"in Malay) her.

Her mother, thinking the two of them were just playing, told the girl that if she wanted to play with her uncle, she should not be crying.

At this point, the man went to the toilet to clean himself.

In the days that followed, the girl complained of pain in her genital area. Her mother assumed she had hurt herself while playing, but when the pain persisted, she sought medical help on March 1 at a polyclinic. The polyclinic then referred the case to the National University Hospital.

The hospital reported the case to the police.

The man was arrested the next day and admitted to sexually assaulting the girl. After his arrest, he was assessed to have an IQ of 61, but was aware that his act was wrong.

Following the abuse, the girl had difficulty sleeping and would wake up crying. She disliked hearing the man's name and described him as "bad" as he had caused her pain, the court heard.

The case was adjourned to next month for the man to be assessed for paedophilic tendencies as well as his risk of reoffending.

A second charge of attempted rape of his 13-year-old girlfriend will be taken into consideration during sentencing.

The maximum punishment for attempted rape is 10 years in jail and caning or a fine.