Meanwhile, Scottish police said "threatening messages" had also been sent to "a number of schools across Scotland".
Dozens of schools in Northern Ireland and Scotland received warnings about a bomb threat on Monday, police and authorities said, with some places reportedly evacuated, even though officials said it appeared to be a hoax.
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"This morning 160 schools received a threat...At this stage the advice to schools is that we're not treating this as a viable threat, but it has clearly caused huge alarm," Northern Ireland Education Minister Paul Givan told reporters.
"It would appear to me (to be) from Islamists threatening that Sharia law will be brought into our country and that there is viable devices within those school settings and it was signed off 'Allah Akbar'," Givan added.
Northern Ireland police said they had received reports "of an email sent to a number of schools across Northern Ireland".
"As a result of this email, police are conducting urgent enquiries, and liaising with the schools in question," police said in a statement.
Local media and Givan said "some schools" had closed as a result.
Meanwhile, Scottish police said "threatening messages" had also been sent to "a number of schools across Scotland".
"These are being treated as a hoax and officers are investigating," Police Scotland said in a statement.
The nature and scale of the messages sent to Scottish schools was unclear.
A politician in Belfast's parliament, Deborah Erskine, said emergency evacuation procedures were initiated at "some local schools" in her constituency in the southwest.