Ontario's Special Investigations Unit headquarters in Mississauga, Ont.. (Colin Perkel / THE CANADIAN PRESS)

The Ontario Provincial Police say they've notified the province's police watchdog to investigate after a man who was being held by Renfrew OPP was injured.

A press release from the OPP says a 21-year-old male prisoner at the Renfrew County detachment suffered an injury at around 11 a.m. Tuesday. The nature of the injury was not disclosed by the OPP.

The man was treated in hospital and returned to OPP custody ahead of a scheduled court appearance.

OPP say they have notified the Special Investigations Unit (SIU), which as invoked its mandate to investigate.

The SIU is a civilian agency that investigates reports involving police where there has been death, serious injury or an allegation of sexual assault.