Nine schools across Northern Ireland were targeted by a threatening email which is thought to be a hoax, police have said.
Several of the schools across counties Antrim, Fermanagh and Tyrone closed due to a "security concern".
Earlier, the Police Service for Northern Ireland said they were liaising with the Metropolitan Police in London over the emails.
The PSNI said they are investigating the circumstances of the threatening email, which was sent to nine schools, and are "at this time, treating the matter as a hoax".
They said they received reports from three schools in Strabane, three schools in Ballycastle and three schools in Enniskillen that they had received an email during the early hours of this morning.
Officers were deployed to each of the schools and the PSNI said: "Checks have not, at this time, resulted in anything untoward at any of the schools".
"Based on inquiries and information to date, police are treating this as a hoax," the PSNI added.
The PSNI's Chief Superintendent Gillian Kearney said such incidents are taken "very seriously", adding inquiries are ongoing.
"We understand the concern in the community, not to mention the disruption it has caused in each of the school communities and for students and parents," she said.
Ms Kearney said the PSNI will "continue to liaise with each of the schools impacted to provide reassurance".
She urged "everyone, in the meantime, to be vigilant and report anything suspicious to police immediately by calling 101, or 999 in an emergency".
Stormont Education Minister Paul Givan condemned the disruption.
In a statement, he said: "I welcome the speedy response from the PSNI who have now assessed the threat and explained to schools they do not need to take any action as a result of this hoax."
Several of the schools impacted posted messages on social media.
Holy Cross College in Strabane, Co Tyrone, said: "Unfortunately the school has had to close today due to a security concern.
"Any children already en route, we would ask that parents make arrangements to collect them.
"We will update you all as soon as possible this morning."
The same message was posted on the Facebook account of Cross and Passion College in Ballycastle, Co Antrim.
Meanwhile, Erne Integrated College in Co Fermanagh posted that the school is "open as normal after the all-clear was given by the PSNI".
'Absolutely disgraceful'
DUP Fermanagh and South Tyrone MLA Deborah Erskine said it was "particularly reprehensible" to target schools.
She said such threats "are to be unequivocally condemned", adding "whilst we await more detail as to their credibility, such threats are unacceptable and have no place in our society".
Ms Erskine commended the leadership of the affected schools "for their swift and responsible response in prioritising the safety and wellbeing of their pupils and staff".
"No child should have their education disrupted in this manner, and no family should have to endure the fear and uncertainty caused by such reckless actions," she added.
The DUP MLA said the "PSNI must act swiftly to identify the culprit behind this".
In a post on X, TUV leader and North Antrim MP Jim Allister said it was "appalling" to see schools closed due to a security threat.
"I trust the police get on top of this situation quickly and that concerns of parents, staff and pupils can be allayed," he said.
SDLP Education Spokesperson Cara Hunter MLA has described the incident as "absolutely disgraceful".
"I cannot understand what would possess someone to engage in this type of activity and it has left many young people, including children, unable to go to school as planned," she said.
Ms Hunter said the "person behind it must be held accountable", adding the "every child must be able to feel safe and secure at school".
A spokesperson for the Education Authority said it was aware of reports of an email sent to schools.
The spokesperson added: "PSNI are conducting inquiries and it would be inappropriate to comment further at this stage."
