A 1998 peace agreement largely ended three decades of violence between predominantly Catholic groups who want a united Ireland and mainly Protestant unionists who want Northern Ireland to remain part of the United Kingdom. But militant splinter groups have stepped up attacks recently.
To prepare for the polling on May 6, extra patrols and vehicle checkpoints are being mounted in the region. Officers have been called on to work additional shifts and those normally behind desks are being put out on the streets.
"We know that in the run-up to the election there are certain elements in society who want to mount attacks on police and to achieve maximum impact," Deputy Chief Constable Judith Gillespie told a media briefing.
"We know there is an intelligence picture which suggests the dissidents are increasing their level of activity."
Since February last year, the threat level has stood at "severe," Gillespie said. "Ever since then, that threat has worsened, so the threat is very, very serious."
Northern Ireland's regional assembly voted last month to take over police and justice powers, cementing the latest hard-won agreement between the province's divided communities, and appointed its first justice minister.
Most of the main Northern Irish paramilitary groups have surrendered their weapons but Republican dissidents such as the Real IRA and the Continuity IRA remain active. They killed two British soldiers and a policeman last year and have carried out several car bomb attacks since then.
Analysts have warned the dissidents might use the British election to draw attention to their cause, with an attack on the British mainland thought to be one their goals. Their capabilities might not allow a strike beyond Northern Ireland but a deadly attack within the province remains an immediate threat.
In recent weeks, dissidents have detonated large car bombs at the army base at Holywood housing the local headquarters of the intelligence service MI5, the courthouse in Newry and the police station in Newtownbutler on the south Armagh border.