Saskatoon police are investigating a sexual assault in the Caswell Hill neighbourhood.

Police say a man approached a 19-year-old woman and assaulted her in a building on 31st Street. They say the victim did not know her attacker.

The woman's injuries are not serious, but she was taken to hospital for follow up care.

No arrests have been made, though police are still investigating. They released a sketch of the suspect. He is described as a First Nations man between 20 and 30 years old, 6"0 with a medium build and short black hair. He was wearing a grey t-shirt and loose-fitting jeans.