Toronto police are asking for help in identifying a man they say sexually assaulted a seven-year-old boy at a west-end subway station.

Police say a woman reported that her son was sexually assaulted from behind while they were on the escalator at Ossington station Wednesday evening.

They say the suspect is between five feet five inches and five feet seven inches tall, with a slim build, and was wearing a grey T-shirt and dark jeans at the time.

Police have released a security camera image of the suspect and are asking anyone with information to contact them.