British Home Secretary Theresa May says attack on British soil a strong possibility
The UK's Security Service MI5 has raised the threat level to Great Britain from Northern Ireland-related terrorism from "moderate" to "substantial".
British Home Secretary Theresa May said the change means a terrorist attack is a strong possibility and reflects the continuing threat from dissident republican activity.
In a statement to the House of Commons, she said the British Home Office was working closely with police and other relevant authorities to ensure appropriate security measures are in place to deal with the raised threat.
The threat level to the UK from international terrorism remains unchanged at severe - meaning an attack is highly likely.
Terror threat levels in the UK can be assessed as low, moderate, substantial, severe or critical - with critical meaning an attack is expected imminently.
The threat to the UK mainland from Northern Irish terrorism was last at substantial in 2011, before it was reduced to moderate in October 2012.
In Northern Ireland - where the threat from home-grown terror has been severe since it was first published in September 2010 - there have been a number of warnings about increased activity from dissident republican groups.
In March, prison officer Adrian Ismay died 11 days after he was injured in a dissident republican bomb attack.