A massive car bomb has exploded outside a courthouse in Northern Ireland, the first such attack in the province for over a decade.

Police have said it was a "sheer miracle" that no-one was killed when a bomb weighing 100kg exploded in the city of Newry on Monday night.

No group has claimed responsibility for the attack but Danny Kennedy, deputy leader of Ulster Unionist party, blamed dissident republicans.

Police said callers using recognised Irish Republican Army code words rang a local hospital and local businesses before ramming the car bomb into the security gates of the courthouse.

Nearby residents reported that the blast made their homes shake like an earthquake, but their windows did not shatter.

Traffic continued to pass by the flaming remains of the car until police shut down the road.

'Reckless and callous'

The blast came some 17 minutes after the call, police said, giving them little time to evacuate the area.

"The time we got to respond was very limited. It was reckless and callous," Chief Constable Matt Baggott said on Tuesday.

Officers say the bomb suggests dissidents are escalating their attacks, three weeks after Northern Ireland's leaders sealed a hard-fought accord to transfer sensitive policing and justice powers from London to Belfast.
 
But British Prime Minister Gordon Brown said Monday's attack will not derail what is the final big step in the process of devolution.

"Such action is, we believe, entirely unrepresentative of the views of the vast majority of people in Northern Ireland," his spokesman said.

"Northern Ireland's politicians have been working incredibly hard to deliver a successful conclusion to the peace process and they will not allow a tiny minority to turn the clock back."

Micheal Martin, the Irish foreign minister, said political leaders would not be distracted from making progress "by a small criminal minority who seek to drag Northern Ireland into the mire of hatred and violence".

Splinter groups

Policing and justice powers are due to transfer from London to Belfast on April 12 and the Northern Ireland Assembly is to vote on the deal on March 9.

Northern Ireland's three decades of violence known as "The Troubles", in which more than 3,500 people died, was largely ended by a 1998 peace deal which paved the way for devolution of power from politicians in London to Belfast.

But there are still splinter groups opposed to the peace process.

Last month a Catholic police officer was seriously injured in a car bomb attack while in September, army experts defused a massive roadside bomb near the border with the Irish Republic in South Armagh.

Last March, republicans shot dead two soldiers at an army barracks in County Antrim and two days later gunned down a police constable as he answered a call for help.