A dog which mauled a five-year-old boy was being shown to schoolchildren as a last day of term treat, it has emerged.
The boy was attacked in the playground of a primary school in Co Antrim this morning.
Raymond Ross, principal of Carniny Primary School on the outskirts of Ballymena, said the animal had unexpectedly "turned" on the schoolboy.
"The dog was in a very controlled position. A number of children had the opportunity to stroke the dog and then suddenly the dog turned on the little child, as if it flicked its head to one side and caught the child in the face," he told the BBC.
Four adults were present at the time of the attack.
The boy was rushed to the Ulster Hospital on the outskirts of Belfast for emergency treatment to facial injuries.
A spokeswoman for the hospital said his family had requested no publicity.
Ballymena Borough Council confirmed the dog had been humanely destroyed this afternoon.
A statement said: "Our thoughts are with the child and his family at this distressing time.
"A representative from Environmental Health attended the school following the incident and, having liaised with those involved, instigated appropriate actions to seize the dog.
"The dog has now been put down.
"Ballymena Borough Council is working alongside all appropriate organisations to carry out a full investigation."
The Health and Safety Executive has also confirmed it has launched an investigation.
Ian Paisley, DUP MP for North Antrim, described the dog attack as shocking.
He said: "It is utterly shocking and very traumatic for the young boy. It shows that we have to be very vigilant when it comes to making sure that dogs are properly tethered at all times.
"My thoughts and prayers go out to the boy and his family."
Meanwhile, a statement from Carniny Primary School said staff had been left shocked.
"We can confirm an incident took place this morning involving a pupil and a dog. The school staff have found the incident to be very distressing. Our thoughts are with the child and his family."
The dog, described as a large terrier type, had been a family pet for a number of years and its vicious reaction was said to be uncharacteristic.
The schoolchildren were allowed to stroke it one-by-one but were closely monitored at all times.
"The class were talking about pets and the teacher said she would bring in her dog to show them at some stage and the children were looking forward to that," said Mr Ross.
"The teacher's husband brought the dog in today in an enclosed playground and the children, from outside the playground, watched the dog play and jump around and they really enjoyed that.
"Very gently then the children were given the chance to come in and stroke the dog in the playground. There were a number of adults present."
Children and many staff left the school at lunchtime today to start their summer holidays.
Mr Ross added: "The children were looking forward to the last day and this was one of the treats that had been offered to them for five or 10 minutes this morning.
"We are just shocked by what has happened. It has been a very distressing day. My sympathy goes to the family of the little child and also to the teacher concerned."
Ballymena councillor James McClean, who lives close to the school, said the community was hoping for good news about the well-being of the boy.
"My thoughts are with his family," he said.