Traffic police decided to run over and kill a dog running around a stretch of motorway in Wales on Monday because it was "the only safe option".
The case will be voluntarily referred to the Independent Police Complaints Commission, which will decide whether or not to investigate the incident.
North Wales police said in a statement that officers were called to a stretch of the A55 between the roundabout at Llanfairfechan and the Conwy tunnel at 3am on Monday after receiving reports of a dog running loose.
The two officers tried and failed to capture the dog, reportedly a foxhound, which was running in and out of traffic, causing a car and a heavy goods vehicle to swerve out of the way while driving at 70mph.
One officer was bitten by the dog while trying to restrain it.
Chief Inspector Darren Wareing said: "The potential for a serious collision was present throughout, and in the circumstances there was no alternative way that officers could contain the dog and minimise risks to motorists.
"The only safe option was to run the dog over at sufficient speed to ensure that it was destroyed and would not suffer. Other methods of destruction were considered, but were ruled out on the grounds of public safety.
"Both officers have their own dogs and did not take this decision lightly. Due to the seriousness of the incident it needed bringing to a conclusion quickly for the safety of all concerned."
The dog was microchipped and police have traced the owner, who lives outside Wales.
Wales Online reported that North Wales police used a Taser on a sheep on the same stretch of road in 2008.
Police said they used the Taser to incapacitate a loose ram that had wandered on to the road at St Asaph, "to ensure the safety of motorists". Unlike in this week's incident however, the animal was unharmed.
In response to high levels of criticism, Chief Superintendent Sacha Hatchett offered a further explanation for the officers' actions in a statement released Wednesday afternoon.
"Officers were forced to make a difficult decision, in difficult circumstances, with their overriding concern being the safety of road users," she said.
"The A55 is a busy road, it's the main route across North Wales servicing the local community and the Holyhead to Ireland ferry crossings.
"At the time of the incident it was dark on an unlit section of road with vehicles, including HGVs, travelling up to 70mph having to swerve to avoid the dog which was dangerously out of control, running across carriageways and head on into oncoming traffic.
"Every effort was made to catch the dog, including officers entering the carriageway and putting themselves at risk. Fearing that the dog was going to cause a serious or potentially fatal collision they took action which they believed to be necessary at the time.
Hatchett added that "the use of firearms was also considered, but ruled out due to public safety" and said people have died in road collisions with animals in the past.
"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 police's handling of the situation was widely criticised on social media.
I'm sorry but, what the fuck North Wales police?! Running over a dog on the A55 because you can't catch it. Disgusting.
Awful decision @NWPolice. There must have been alternatives. "Police run over dog on A55.....on purpose" https://t.co/IQ6IF7VVz0
The police statement has been shared nearly 7,000 times on Facebook and attracted some strongly worded comments.
Others conceded that ultimately the police's job is to save lives and prevent accidents.
I'll be blunt & truthful, if a single human life was spared & other options considered, I'd vote @NWPolice on this https://t.co/EvC5oVpOrt
The Independent Police Complaints Commission said in a statement: "North Wales Police has advised the IPCC that it will be referring this incident to us. We await the referral later today, and will then assess it to determine the level of involvement needed by the IPCC in any investigation."