Hoax bomb calls were made to seven primary schools in Northern Ireland yesterday, prompting a number of evacuations.
Similar malicious communications were made to schools elsewhere in the UK on Monday and police services are working together to establish if there is a link.
Officers said they have no information to indicate a terrorist link to the incidents.
PSNI Chief Superintendent Garry Eaton said: “Between 9am and 10am the schools, all of which were primary schools, received calls claiming explosive devices had been placed at each location.
“Local police responded immediately, working with the individual school authorities to establish what the circumstances of the calls were and to put appropriate procedures in place to ensure the safety of both pupils and staff.
“This was obviously a very serious and worrying situation, particularly for the parents of pupils at the schools, however after thorough police searches of all of the schools, no devices were found.”
Commenting on the alerts in Great Britain, Mr Eaton said: “A link is obviously a strong line of inquiry and we will be working closely with our colleagues in the other police services concerned to establish if there is any definite connection between their calls and ours.”
The principal of a Coleraine school has condemned a malicious phone call made to Ballysally Primary yesterday morning.
Principal Geoff Dunn said a male had made the threatening call to the school – which should have been a “safe haven for so many children”.
He said: “It was a disgrace that there was a threat put on the school – but the children and the staff were amazing.”
Mr Dunn added: “The whole community in Ballysally came together. A local Presbyterian church opened its doors so the children could use the facilities and one of the local shopkeepers brought down biscuits and juice free of charge.”