The terror threat level in Northern Ireland has been raised to ‘severe’ following an uptick in activity by a “small number” of dissident republicans determined to use “politically motivated violence”.
MI5 increased the threat from ‘substantial’ to ‘severe’, which means that an attack is highly likely. The intelligence service, which makes assessments independent of ministers, urged the public to remain “vigilant" but "not be alarmed".
The move comes after a series of incidents targeting security forces in Northern Ireland, including the attempted murder of detective chief inspector John Caldwell in Omagh last month.
The threat level for the rest of the UK remains at ‘substantial’, meaning an attack is considered ‘likely’. Northern Ireland’s level had been lowered to substantial a year ago - the first time it had been altered since 2010.
In a written statement to MPs, Mr Heaton-Harris said MI5 had increased the threat level to the region from Northern Ireland-related terrorism independently of ministers.
"The public should remain vigilant, but not be alarmed, and continue to report any concerns they have to the Police Service of Northern Ireland," he said.
He said that despite the success of the Good Friday Agreement "a small number of people remain determined to cause harm to our communities through acts of politically motivated violence".
"In recent months, we have seen an increase in levels of activity relating to Northern Ireland related terrorism, which has targeted police officers serving their communities and also put at risk the lives of children and other members of the public.
"These attacks have no support, as demonstrated by the reaction to the abhorrent attempted murder of DCI Caldwell."
Mr Caldwell was shot a number of times at a sports complex in Omagh, Co Tyrone, after coaching a youth football team.
He remains in a critical but stable condition more than a month on from when he was attacked.
At the end of February, a typed message was posted on a wall in Derry/Londonderry purportedly from the New IRA, claiming responsibility for Mr Caldwell’s attempted murder.
Detectives have arrested 10 men in connection with the attempted murder but no one has been charged in relation to the shooting.
The tenth suspect was detained in the Belfast area under the Terrorism Act on Tuesday 14 March.
Simon Byrne, chief sonstable of the Police Service of Northern Ireland, said: "This is part of an ongoing process of monitoring the threat level in Northern Ireland, which is conducted by MI5.
“We have spoken publicly about the number of attacks that have taken place in recent months, not least the attempted murder of DCI John Caldwell on 22 February.
"We will relentlessly pursue those who seek to cause harm and terrorise our communities, and attack my officers and staff, and I pay tribute to them as they continue to deliver for our communities.
"I would also like to thank the community and political leaders of Northern Ireland for their overwhelming support for the Police Service in recent times."