There were no reports of serious injuries and no one had claimed responsibility for the attack, a police spokeswoman said.

Local politicians said about 50 local residents had been evacuated to a community hall after the authorities received telephone warnings of the bomb.

A Protestant politician, Basil McCrea, said one man was hospitalised suffering from suspected shock after he was "blown off his feet" by the shockwave.

Politicians agreed the attack appeared timed to undermine Britain's transfer of policing and justice powers to a new justice department in Northern Ireland's power-sharing administration.

Policing powers

Northern Ireland endured three decades of civil strife between Catholics who wanted the province to become part of the Republic of Ireland and Protestants who wanted to stay within the United Kingdom.

The blast came as the Belfast administration resumed policing powers [EPA file]

The violence largely ended with the signing of the 1998 Good Friday peace accords, which paved the way for the current power-sharing administration between the Protestant DUP and the Catholic Sinn Fein parties.

The main paramilitary groups, including the IRA, have laid down their arms, but sporadic violence – usually blamed on dissident groups opposed to the peace process - still plagues the province.

The policing and justice powers were transferred from London to Belfast at midnight on April 12, resolving one of the most sensitive issues in Northern Ireland.

When legislators approved the power transfer deal last month, Gordon Brown, the British prime minister, hailed it as the "final end" to decades of conflict.

"The completion of devolution... is the final end to decades of strife. It sends the most powerful message to those who would return to violence: that democracy and tolerance will prevail," Brown said.

At the height of the violence known as "The Troubles" in 1972, the British government led by Edward Heath, the then prime minister, seized control of policing and justice from Northern Ireland's local ministers in a bid to control the worsening security situation.

But the move prompted the fall of the devolved administration and the powers remained with London throughout the conflict, in which more than 3,500 people died.