Northern Ireland’s terror threat level has been raised from substantial to severe as the likelihood of attack by dissident republicans appears high.

Based on an MI5 intelligence assessment, the announcement an escalation of extremist activity, including the recent gun attack on a top police officer.

The province is soon to mark 25 years since the Good Friday Agreement which cemented a lasting peace after decades on civil conflict.

Despite the Provisional IRA coalescing behind its democratic political wing , Sinn Fein, a small number of hardline republican splinter groups have remained fiercely opposed to the accord.

Authorities could be anticipating that dissidents will seek to mark the anniversary with a terror attack.

The downgrade in Northern Ireland’s terror threat level was made last March – its first change for 12 years.

It was announced by Northern Ireland Secretary Chris Heaton-Harris.

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His statement said: “The threat level to Northern Ireland from Northern Ireland Related Terrorism is constantly monitored and is subject to a regular formal review.

“This is a systematic, comprehensive and rigorous process, based on the very latest intelligence and analysis of factors which drive the threat. The threat level review takes into account a range of factors and analysis of recent incidents.”

He later added: “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. However, 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.

“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.”