Dissident republicans are being blamed for a car bomb which exploded outside Newry courthouse in Co Down last night.
The PSNI said it was a "sheer miracle" that no-one was killed or injured in the attack which took place after a number of telephone warnings.
Police have downgraded their estimate of the size of the device from up to 800lbs (363 kilos) and said it could have been approximately 250lb.
The car containing the bomb was left at the gates of Newry courthouse at 10pm last night and police officers were notified of the suspicious vehicle a few minutes later.
A number of warnings were then telephoned to a local hospital and businesses. The first warning was received by the local hospital at 10.20pm and a business in the town received a further warning at 10.22pm. The PSNI was in the process of evacuating the area when the device detonated at 10.37pm.
The area surrounding the courthouse has been sealed off for a technical examination.
Classes at nearby Windsor Hill Primary School were cancelled today and a 170-year-old church was damaged by the force of the explosion. Investigators are searching the roofs of nearby houses while others are picking throught the remnants of the exploded car, now barely a charred shell, and other material off the road.
The gates of the courthouse and a security hut were badly damaged but the building itself is thought to be largely intact.
Police are this evening responding to further bomb alerts in north Belfast and in Lurgan, Co Armagh.
Questioning the motives behind the Newry attack this afternoon, PSNI Chief Constable Matt Baggott condemned the bombers and the time given to officers to clear the area.
"There is absolutely no excuse for bringing bombs on to our streets in any shape or form but added to that the time in which people were given was severely limited," he said. "This is not an attack on a court building. This is an attack on people whose lives depend on the well-being of Newry.
"This is an attack that broke and damaged places of worship. This is an attack that has damaged the ability of Newry to be at the heart of our economic success," he added. "This is much, much more than simply an attack on a court building and this is exactly what these people want. They have no plan except a breakdown."
The attack has been condemned by nationalist and unionist politicians.
Sinn Féin’s Conor Murphy heard the blast while in his home more than six kilometeres away. “We can only be thankful that at this stage it appears nobody has been injured,” he said.
“The people responsible have absolutely nothing to offer the community except the prospect of a return to the past. A lot of good people have worked long and hard to develop Newry over the last 10 years and this will be a major blow to the city. The community will be despairing tonight but they will be determined not to let this beat them.”
Last night's attack came only three days after a failed mortar bomb attack at a police station in the nearby village of Keady, Co Armagh and weeks after Sinn Féin and the Democratic Unionists agreed a landmark deal on the devolution of policing and justice powers that saved the powersharing executive from possible collapse.
Last March, dissidents killed two British soldiers at Massereene army barracks, Co Antrim. Two days later they shot dead police constable Stephen Carroll in Craigavon, Co Armagh as he answered a call for help.
In January this year a Catholic police officer was seriously injured when a booby trap bomb exploded under his car in Co Antrim while a number of police stations have been shot at in recent weeks.
Additional reporting: PA
