There have been widespread appeals for calm across Northern Ireland amid fears that a major explosion blamed on dissident republicans was intended to ramp up tensions ahead of the Twelfth.
The PSNI said the roadside bomb, which destroyed a small bridge in south Armagh, was designed to kill its officers when it exploded on Saturday.
Large piles of rubble and a huge crater were left after the “significant” device destroyed part of a country road and bridge between Belleeks and Cullyhanna.
Superintendent Pauline Shields described the attack as a “callous and blatant attempt to kill and injure policemen”.
She said it illustrated the “extremely high threat” to police from dissident republicans.
No-one was injured in the 5.30pm explosion but police were yesterday working “with extreme caution” in follow-up searches.
The attack has sparked fears that dissident republicans are trying to escalate community tensions ahead of today’s Twelfth celebrations.
Superintendent Shields said: “We believe there is currently no real risk to members of the public; this is a small, isolated country road. But there is a real risk to my officers. That is why we have to assess the situation and take the right action to keep both the community and my officers safe.
“However, we are doing everything in our power to keep them safe and to investigate the incident.”
Justice Minister David Ford condemned the weekend blast.
“The days of the bomb and the bullet are in the past and thankfully no one was injured in this blast which was an attack on the entire community and designed to kill, maim and frighten,” he said.
Sinn Fein MP for Newry and Armagh Conor Murphy, said: “This bomb could have seriously injured local people travelling on this road, a fact which the perpetrators seem to have ignored.”
Meanwhile an investigation was launched last night after reports that a bomb had been abandoned in Co Fermanagh.
A spokeswoman for the PSNI said officers had received information claiming terrorists had left a device on the Rosslea to Brookeborough Road.
Members of the public were urge to be vigilant and warned not to touch anything that looked suspicious but to report it to police immediately.
Officers were being cautious in case the warning was an attempt to lure them into a trap.
Ulster Unionist MLA in the area Tom Elliott said: “Clearly it is dissident republicans at their evil deeds and whether it is a hoax or something deliberate remains to be seen. They are trying to disrupt things coming up to the Twelfth which is being held in Brookeborough.”
In north Belfast, there are fears of trouble ahead of a contentious feeder parade passing through the flashpoint Ardoyne area today.
Assistant Chief Constable Alistair Finlay said: “We would appeal to key people with influence in both communities to continue to work to ensure that this parade does not escalate into disorder.”