A dog running loose on a motorway was run down and killed by traffic police deliberately because of fears it would cause a serious crash.

Despite attempts by the Roads Policing Unit to catch the dog, it continued to run in and out of swerving traffic that was travelling in excess of 70mph on an unlit carriageway.

The incident - which had "potential for a serious collision" happened during the early hours of Monday. An officer who had tried to take hold of the dog was bitten.

In a statement issued on their website the force said that the dog had been running loose on the A55 at varying locations between the Llanfairfechan roundabout and the Conwy tunnel.

Chief Inspector Darren Wareing said that several calls were received by the North Wales Police control room shortly after 3am and the decision to take action was not taken "lightly".

He said: "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." Mr Wareing said that several attempts were made to catch the dog.

"One car and an HGV had to swerve to avoid the dog whilst the officers remained on foot in the carriageway," he added. "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."

"Fast roads such as the A55 present inherent risks, and to have vehicles including an HGV having to swerve in the dark was deemed unacceptable as the officers witnessed a number of near misses, and were highly concerned about the potential aftermath of a high-speed collision.

"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."