The terror threat level in Northern Ireland has been raised from "serious" to "severe", the British government have confirmed.
The latest update means that the government believe an attack is "highly likely" to occur.
Britain's Northern Ireland secretary Chris Heaton-Harris confirmed the ruling by MI5, the UK's security service, in a statement to his fellow MPs.
He said: "MI5 has increased the threat to Northern Ireland from Northern Ireland Related Terrorism from 'SUBSTANTIAL' (an attack is likely) to 'SEVERE' (an attack is highly likely).
"The public should remain vigilant, but not be alarmed, and continue to report any concerns they have to the Police Service of Northern Ireland (PSNI).
"Over the last 25 years, Northern Ireland has transformed into a peaceful society. The Belfast (Good Friday) Agreement demonstrates how peaceful and democratic politics improve society.
"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.
"I pay tribute to the tremendous efforts of the Police Service of Northern Ireland and security partners, and the determination and resilience of the Northern Ireland people, who are making Northern Ireland a safer place to live and work. The political future of Northern Ireland rests with the democratic will of the people and not the violent actions of the few. Together we will ensure there is no return to the violence of the past."
PSNI Chief Constable Simon Byrne 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 February 22.
“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.”
Justice Minister Simon Harris has said the increase in the threat level in the North is "concerning and regrettable" a year after the level was raised from moderate to substantial.
Speaking at Government Buildings on Tuesday, Minister Harris said despite ongoing and significant work on the peace process "there remains to this day a real threat" to peace in Northern Ireland.
Addressing terrorist, paramilitary groups, he said those behind the threats are "morally vacant" and that people "should never lose sight of that".
Mr Harris said he has been assured by Garda Commissioner Drew Harris that the threat of an attack from such groups in Ireland is generally considered to be low.