The UK’s MI5 security service on Tuesday raised the terror threat level for Northern Ireland from “substantial” to “severe”, indicating that a terrorist attack on the devolved region of the country is not just likely but highly likely.

The change comes ahead of a planned visit by US President Joe Biden to mark the 25th anniversary of the Good Friday Agreement next month, which brought peace to the region after decades of violence.

The Northern Ireland Secretary, Chris Heaton-Harris, told the House of Commons that the decision was made by MI5 – the UK’s counter-intelligence agency – independent of ministers.

It reverses a downgrade in Northern Ireland's terror threat level in March last year, the first change in 12 years for the region with a history of sectarian conflict.

The move to raise the terror threat level, based on an MI5 intelligence assessment, follows a rise in dissident republican activity, including a recent gun attack on a top police officer.

“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),” Heaton-Harris said.

"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)," he said.

“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,” said Heaton-Harris.

“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,” he added.

The threat level for the rest of the United Kingdom remains at "substantial", meaning an attack is considered likely.

The UK operates a five-pronged threat alert system: low -- an attack is highly unlikely, moderate -- an attack is possible, but not likely, substantial -- an attack is likely, severe -- an attack is highly likely and critical -- an attack is highly likely in the near future.

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