The UK has raised the terror threat level from Northern Ireland from moderate to substantial, meaning there is a "strong possibility" of an attack. The Home Office announced the terror threat level has been raised in order to reflect the "continuing threat from Dissident Republican activity".
The Real IRA recently claimed responsibility for the murder of Belfast prison officer Adrian Ismay, who died from his injuries 11 days after a bomb was detonated underneath his van on 4 March. The New IRA claimed it was targeting training officers working at the Maghaberry Prison near Lisburn, County Antrim as part of its plan to "take the war to the age-old enemy of our nation".
The five terror threat levels range from low, meaning an attack is unlikely, to critical, meaning an attack is imminent. The UK is currently on a level three substantial risk of attack from Northern Ireland.
Home secretary Theresa May said: "The main focus of violent dissident republican activity continues to be in Northern Ireland where they have targeted the brave police and prison officers who serve their communities day in and day out.
"The reality is that they command little support. They do not represent the views or wishes of the vast majority of people, both in Northern Ireland and the Republic of Ireland, who decisively expressed their desire for peace in the 1998 Belfast Agreement and have been transforming Northern Ireland ever since.
"However, it is sensible, given their stated aims, that the public in Great Britain should also remain vigilant and report any suspicious activity to the police. But we should not be alarmed, and this should not affect how we go about our daily lives."
The Police Service of Northern Ireland (PSNI) said the rise in terror threat level is a result of the MI5's "most up to date assessment of the continuing threat from dissident republican activity".
PSNI assistant chief constable Will Kerr said: "We are aware of the announcement in parliament today that the threat level in Great Britain from Northern Ireland-related terrorism has been increased from 'moderate' to 'substantial'.
"Threat levels are kept under constant review and today's announcement by the home secretary is about increasing awareness and encouraging vigilance. I would ask the public, as always, to remain vigilant and report any suspicious activity to police. Providing such detail to police is vital and helps us protect our communities. It isn't informing, it's enabling us to keep you and your community safe."