PELHAM, Ont. -- A police officer was shot multiple times during an argument with his fellow officer in an incident in the Niagara region, Ontario's police watchdog said Friday as it announced new details of its probe of the incident.

The Special Investigations Unit is probing the shooting, which occurred in Pelham, Ont., on Thursday at noon that involved officers from the Niagara regional police.

The Niagara police were investigating a car crash that happened days earlier when the two officers got into an altercation, SIU spokeswoman Monica Hudon said in a statement Friday.

"One officer discharged his firearm multiple times, and the other officer was struck," she wrote. "The officer who was struck was transported to hospital where he is in stable condition."

Twelve other officers who were nearby will be treated as witnesses, she said.

The SIU said the injured officer is a 52-year-old man, and Niagara police said he had served 28 years on the force, but officials declined to identify him further.

"The days and weeks ahead will be trying ones for the NRPS family and the community we serve," said Niagara regional police Chief Bryan MacCulloch. "I ask for your support for our members and all those involved."

The region's police services board said in a statement that it was "deeply concerned" by the shooting, but that it couldn't comment further until the SIU had completed its probe.

Hudon said the SIU had assigned 11 investigators, including three forensic specialists, to the case. She said it's very early in the investigation and there have been no arrests.

She urged anyone with information -- particularly anyone with video evidence -- to contact the SIU.

The Ontario Provincial Police has been called in to investigate other aspects of the incident that fall outside of the watchdog's jurisdiction. A provincial police spokeswoman declined to comment on its investigation.

The SIU is an arm's-length agency that is automatically called in to investigate reports involving police where there has been death, serious injury or an allegation of sexual assault.