Hundreds of schools in Northern Ireland, Scotland, Hungary and Serbia were sent bomb threats on Monday, with some evacuated as authorities said the warnings appeared to be a hoax.
It is not yet known whether the incidents were connected to each other.
“Police investigating the circumstances of threatening emails sent to schools across Northern Ireland this morning … are treating the matter as a hoax,” authorities said.
Northern Ireland police said up to 300 schools had received “the same emailed message which contained a generalised threat” which was also received by “some schools across the UK”.