The threat level from Northern Ireland-related terrorism in Great Britain has gone up from moderate to substantial.
It means an attack in England, Scotland or Wales is “a strong possibility”.
Home Secretary Theresa May said the level, set by security service MI5, “reflects the continuing threat from dissident republican activity”.
The level for Northern Ireland-related terrorism in Northern Ireland remains “severe”, meaning an attack is “highly likely”.
Mrs May confirmed the change of threat level relating to Great Britain – meaning three of the four countries of the UK – in a written statement to Parliament.
“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,” she wrote.
The public should “remain vigilant and report any suspicious activity to the police”, she added.
At Easter the New IRA, the group responsible for the murder of prison officer Adrian Ismay in March, warned that its members were “determined to take the war to the age-old enemy of our nation”.
The threat level for Northern Ireland-related terrorism in Great Britain was raised from moderate to substantial in 2010, then reduced back to moderate in 2012.
The threat level to the UK from international terrorism is currently set at severe. For this measure, Northern Ireland is not rated separately.
Source:: BBC UK