A police force is under investigation after traffic officers deliberately ran down and killed a dog that was loose on a dual carriageway.
North Wales Police has referred itself to the Independent Police Complaints Commission following thousands of complaints after officers took the "difficult decision" to run over the dog which was "dangerously out of control".
The dog was loose on an unlit section of the A55 near Llandudno in the early hours of Monday, where it was spotted running across carriageways and towards oncoming traffic, forcing cars and lorries travelling at speeds of 70mph to swerve to avoid it.
Every effort was made to catch the trail hound, the force said, with officers going on to the road and putting themselves at risk, but a decision was made to destroy it - carried out by two officers who both own dogs.
The same force previously Tasered a sheep on the same road after it disrupted traffic. The ram was incapacitated and survived, but the RSCPA investigated.
The killing of the dog has drawn widespread criticism but was backed by its owner, police said, who was "devastated" but understood the decision.
Chief Superintendent Sacha Hatchett said: "He said he appreciates that given the risk to human life, the officers made the correct decision. He is supportive of the police as had there been a serious accident, he said he could not have lived with himself."
But there were accusations of "animal cruelty" and calls for those responsible to face criminal charges among the 15,000 comments on the force's Facebook page.
Pauline Bennett wrote: "Would the outcome have been the same if it had been a child running in and out of traffic? Does it make it better that the officers are dog owners, I think not."
Shelagh Davies said: "Should have stunned it with a tranquiliser, at least it would be still alive."
But others defended the officers' actions, suggesting they had no choice.
Gabrielle Reay wrote: "Option of killing a dog or stopping a serious accident... no brainer to me," while James Dykes said: "The police had a tricky decision to make but made one and it was one dog and not a poor family killed on their way back from holiday swerving to avoid it."
Peter Evans, a former motorway police officer, added: "Motorists will do anything, usually stupidly, to avoid killing a dog, and that's where the danger lies. If a multiple fatal pile-up had occurred as a result of this dog, then that would be the fault of the police too. A very difficult decision to make."
The RSPCA called it a "tragic incident" and said it would be contacting North Wales Police, while animal rights charity Peta condemned the killing.
Peta director Mimi Bekhechi said: "This could just as easily have been a frightened human being or someone with a mental illness. These officers desperately need a crash course in humane animal control if they believe that crushing a dog under a vehicle was the best or only available option."
Ms Hatchett defended the officers, saying it was "a difficult decision", with their "overriding concern being the safety of road users".
She said: "It was a fast-moving incident, officers at the scene were in contact with the force control room and other options were considered. Officers used their vehicle to partially close the road, the use of firearms was also considered, but ruled out due to public safety.
"Regrettably the urgency of the situation meant that the decision was made by the officers at the scene to take the action that they did."
She added: "At times we are called upon to destroy animals in the course of our police duties, and such decisions are never taken lightly. This decision was not taken lightly.
"In North Wales we have had people lose their lives in collisions caused by animals running loose on the road. We understand that people are upset that a dog was killed, the officers are also upset, it is regrettable, but we will never know what could have happened had such action not been taken.
"The force has voluntarily referred the incident to the Independent Police Complaints Commission because of the level of public concern. It is also being reviewed by the force to ensure we examine options available to officers and we will liaise with RSPCA Wales and others in doing this."
North Wales Police and Crime Commissioner Winston Roddick said it was a "difficult judgment to make" and said he would be raising the incident with the force.