Britain raises Irish terror threat
The British government has raised the threat from Irish-related terrorism from moderate to substantial, meaning an attack is a "strong possibility".
It is the first time that this threat level has been published, officials said.
The threat to the country from international terrorism remains severe.
British home secretary Theresa May said: "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."
The head of MI5 warned last week that dissident Irish republicans could attempt to mount a new wave of terrorist attacks on the British mainland.
Jonathan Evans, the director-general of the Security Service, said there had been a "persistent rise" in "activity and ambition" by dissident groups in Northern Ireland over the past three years. While they did not have the capacity to return to the levels of violence caused by the Provisional IRA at the height of the Troubles, he said they still represented "a real and rising security challenge".
His warning came after the Real IRA publicly threatened to target banks and other financial institutions in the City of London, accusing them of "financing Britain's colonial and capitalist system".
In his speech, Mr Evans acknowledged that the recent rise in activity by dissident republicans had not been foreseen, having been assumed just three years ago to be "low and likely to decline further".
"Perhaps we were giving insufficient weight to the pattern of history over the last hundred years, which shows that, whenever the main body of Irish republicanism has reached a political accommodation and rejoined constitutional politics, a hard-liner rejectionist group would fragment off and continue with the so- called 'armed struggle'," he said.
Since the start of the year, however, there had been more than 30 attacks or attempted attacks on national security targets by dissident republicans, compared with just over 20 for the whole of last year, he said. At the same time, there were increasing signs of co-operation and co-ordination between the various groups, deploying a greater variety of attack techniques with improved weapons capability - including Semtex explosives associated in the past with the Provisional IRA who are now on ceasefire.