Alberta's police watchdog has been directed to investigate after a man was found dead in a Calgary jail cell.

Police responded to Marlborough CTrain Station at Eighth Avenue and 36th Street N.E. for a report of a man with an airsoft gun.

Officers found the man and arrested him without any incident. The arrest was captured on police body-worn camera, the Alberta Serious Incident Response Team said in an emailed release.

The man was charged with offences related to a breach and taken to the Spyhill Services Centre in northwest Calgary where he was cleared by a medic and placed in a holding cell.