MI5 has raised the threat level to Great Britain from Northern Ireland-related terrorism from moderate to substantial, Home Secretary Theresa May has said.
The Security Service increased the level from moderate to substantial - which is the third most serious category out of five and means a terrorist attack is seen as a "strong possibility"
May said the level of the threat "reflects the continuing threat from dissident republican activity".
The level for Northern Ireland-related terrorism in Northern Ireland remains at severe, meaning an attack is "highly likely".
In a statement to the House of Commons, she said: "As a result of this change, we are working closely with the police and other relevant authorities to ensure appropriate security measures are in place."
At Easter the New IRA warned that its members were "determined to take the war to the age-old enemy of our nation".
The BBC reported that the threat level for Northern Ireland-related terrorism was raised from moderate to substantial in 2010, then reduced back to moderate in 2012.
The threat level to the UK from international terrorism remains at severe - meaning an attack is "highly likely". This has not been changed.
May said the threat level to Northern Ireland from Northern Ireland-related terrorism is also unchanged at severe.
She added: "The public should remain vigilant and report any suspicious activity to the police."