The security services believe dissidents pose a greater threat
The government and security services believe dissident republicans pose a greater threat than ever.
The threat assessment has been raised to "severe", meaning an attack is regarded as highly likely.
The decision to upgrade the level was made by MI5 - responsible for gathering intelligence on dissident republicans.
For a number of years now the threat posed by dissidents was "substantial", meaning attacks were regarded as a strong possibility.
While dissident groups remain relatively small and do not have a central command structure - intelligence information suggests groups in some areas are becoming much better organised and more technically sophisticated.
Their level of activity has also increased.
Security sources have said that police have prevented a large number of planned attacks in recent months.
But the determination to carry out attacks has increased, and the police and security services are having to work much harder to stop them.
BBC Northern Ireland's Home Affairs Correspondent Vincent Kearney reports on the new threat level.
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