The raising of the threat level from dissident republicans is “worrying”, Northern Ireland First Minister Peter Robinson has said.
The threat level posed by dissidents in Britain had been scaled up from “moderate” to “substantial”, the Home Office in London warned yesterday.
Using intelligence from the security service, home secretary Theresa May said the possibility of dissident republican violence carried out in Britain was now "a strong possibility".
"The director general of the security service has informed me that he has raised the threat to Great Britain from Irish-related terrorism from moderate to substantial, meaning that an attack is a strong possibility," she said.
"Judgments are based on a broad range of factors, including the intent and capabilities of terrorist groups.
"This is the first time we have published the Irish-related threat assessment to Great Britain. This is in the interests of transparency and to encourage people to remain vigilant."
The first and most important duty of government was the protection and security of the British people, she said.
"We have been consistent in stating that the threat to the UK from terrorism is real and serious. The balance we aim to strike is keeping people alert but not alarmed. I would urge the public to report any suspicious activity to the police and security services in their continuing efforts to discover, track and disrupt terrorist activity."
Last week MI5 director-general Jonathan Evans said there had been a "persistent rise" in activity and ambition by dissidents since 2007. However, he added that while they posed a "real and rising" security challenge, they did not have the capacity to match the violence carried out in Britain during the Troubles.
It was pointed out last night that the principal security threat to Britain is posed by international terror groups rather than dissident republicans.
Minister for Justice Dermot Ahern responded last night saying: "We continue to devote substantial resources to counteract the threat which so-called dissident republican groups represent and there are unprecedented levels of co-operation between the security services in the two jurisdictions."
At Stormont First Minister Peter Robinson said: "The dissident republican terrorist organisations have no support within the wider community in Northern Ireland.
"The continued existence of such groups is in direct defiance of the wishes of the people of Northern Ireland who have expressed clearly their desire for peace and stability. It is a worrying sign that the intelligence services have upgraded the threat level, which underlines the need for adequate police resources to tackle this threat and stamp it out completely."
SDLP leader Margaret Ritchie accused the British intelligence service of not being up to the job of monitoring dissident groups and insisted MI5 had a "mainland mentality".
"The threat level against our people and our police officers has been substantial to severe for a long time but MI5 did little enough about it," she alleged.