Two schoolgirls from Cwmcarn High School have been arrested on suspicion of conspiracy to commit murder.
Media reports suggest the target of the plot was a teacher, but no one was harmed and the matter was resolved peacefully.
Gwent Police said the teenagers were arrested at the school on Thursday following concerns about their behaviour.
The pair have been released on bail pending further inquiries.
Police said a 15-year-old pupil, from Newbridge, was arrested on suspicion of threats to kill, possession of a bladed article on school premises and conspiracy to commit murder.
The second girl, from Risca, was arrested on suspicion of conspiracy to commit murder.
In a statement on the school’s website, Headteacher Jacqui Peplinski said: “Please be assured that the concerns were dealt with swiftly.
“There was no risk to any staff or learner and the relevant support services were contacted as a precautionary measure.
“Cwmcarn High is a caring and safe environment and we are committed to everyone’s safety. Please do not hesitate to contact us if you have any concerns.”
The alleged murder plot comes less than a week after Ann Maguire, 61, died following a classroom attack at Corpus Christi Catholic College in Leeds.