Police investigating an alleged sexual assault of a teenage girl in Sydney's western suburbs earlier this year have released CCTV vision of a man they want to speak to.

Detectives from the State Crime Command’s Child Abuse and Sex Crimes Squad have been investigating the alleged sexual assault of a 15-year-old girl in the Belmore and Campsie areas on March 26.

Police wish to speak to a man they believe can assist them with inquiries into the sexual assault of a teenage girl. Credit:NSW Police

A police spokeswoman said the girl did not know the man but had encountered him briefly on a previous occasion.

On the day of the alleged assault, the pair met again in the area of Belmore train station. The meeting was not prearranged, the spokeswoman said.