Paralympic champion Oscar Pistorius has been accused of making a "sinister" comment to a friend of his late girlfriend Reeva Steenkamp during his murder trial.

The double amputee is being tried for the alleged murder of Steenkamp, whom he shot dead through a bathroom door at his home in Pretoria, South Africa on Valentine's Day last year.

Kim Myers, who is said to have been present numerous times throughout the trial, has accused Pistorius of approaching her during an adjournment at the High Court.

Myers's lawyer Ian Levitt told Reuters on Tuesday: "During an adjournment in court today, my client Kim Myers was approached by Oscar Pistorius, who whispered in a sinister undertone, 'How can you sleep at night?'

"She is horrified by this disturbing act, but will not be intimidated and intends to carry on attending the trial for Reeva."

Local reports have claimed that the athlete, who competed in both the Olympic and Paralympic Games in London 2012, refuted suggestions that the incident occurred when he was approached by journalists at the court.

Pistorius denies murder by maintaining that he mistook Steenkamp for an intruder when he fired the shots.