Darrel Campbell disarmed the alleged attacker after two other staff members and a pupil were stabbed at Ysgol Dyffryn Aman in Ammanford on Wednesday morning.

All three victims have now been discharged from the hospital following the incident, according to Dyfed-Powys Police. A teenage girl has been arrested on suspicion of attempted murder.

Mr Campbell, who intervened, has worked at the Carmarthenshire school for 40 years, according to his brother Cefin Campbell, the Senedd member for Mid and West Wales.

Speaking to the PA news agency about his brother's actions, the politician said: "He [Darrel] is embarrassed by all the attention that he's had, he certainly doesn't consider himself a hero in any way.

"He just told me he just did what most people would have done - he acted instinctively, he saw the danger and took action.

"He really wants to play down anything more than just being a normal citizen, albeit a teacher in a school facing a very challenging situation."

Dyfed-Powys Police said the incident happened at about 11.20am on Wednesday morning.

The force confirmed the school was put into lockdown "for the safety of all on the premises".

Pupils were released from the school at around 3.20pm, with hundreds of parents gathered outside to collect them.

The comprehensive school in the town of Ammanford in Carmarthenshire has around 1,500 pupils between the ages of 11 and 18.

Headteacher James Durbridge said the school would provide wellbeing support to all affected.

He described it as a "very difficult day" for the school, and said that his thoughts were with the three people injured, and their families.

The school did not open on Thursday to allow police to continue their investigation.

'Shocking incident'

Superintendent Ross Evans, Carmarthenshire Commander, said police were working with the school and other agencies to ensure "appropriate support is available to all involved".

"We urge anyone affected by yesterday's events to seek support, and not to share any videos, photos or information that might cause further distress to pupils or parents at the school," he said.

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Leader of Carmarthenshire County Council Darren Price praised the teachers, staff and pupils of Ysgol Dyffryn Aman "for the way they've responded to this shocking incident".

"As a council, our priority now is to do all that we can over the coming days and weeks to support the pupils and staff in the aftermath," he said.

Meanwhile, another teenager from the Cross Hands area, about five miles away, has been arrested on suspicion of making threats, which referred to the incident at Ammanford.

Police executed a warrant at his home following reports about threatening messages being sent on social media, which led to him being taken into custody in the early hours of this morning.

Supt Evans added: "We would like to thank the many members of the public who reported concerns around messages they had seen online. This allowed us to take swift action in executing a warrant and arresting a suspect.

"While this investigation is being run separately to our enquiries into the major incident at Ammanford yesterday, our officers will be seeking to establish both the credibility of the threats, and whether there was any connection between the alleged offences.

"Again, I would urge people not to speculate, not to share any images or videos relating to either investigation, and to allow us to carry out our enquiries fully."