A man who sexually assaulted a young girl in front of her two siblings had denied he attacked a teenage girl when questioned by police 14 months earlier, a Perth court has been told.

Sean Wood, 51, appeared in the WA District Court for sentencing on Wednesday charged with several sexual offences, including the assault on the 15-year-old girl in August 2017.

WA District Court. Credit:Emma Young

The court was told Wood was standing in a laneway near Clifton Crescent in Mount Lawley in the early hours of the morning when he approached the girl who walked past.

He grabbed her from behind, smothered her mouth and whispered: “If you scream I will kill you.”