A car bomb planted outside a Northern Ireland police station by dissident republicans was defused on Tuesday, police said, a day after a bomb exploded near the headquarters of the British intelligence services.

In a call to local media, the Continuity IRA, which last year killed a police officer in the bloodiest three days in Northern Ireland for more than a decade, claimed responsibility for planting the bomb in the county of Armagh.

The Real IRA, a dissident group which also opposes Northern Ireland's peace process and killed two British soldiers two days before the killing of the police officer, exploded a bomb near the offices of Britain's domestic spy agency MI5 on Monday.

The attacks coincided with the moving of police and justice powers from London and the appointment of Northern Ireland's first justice minister, the final piece of a devolution process begun by a 1998 peace deal between pro-Irish Republicans and pro-British Unionists.

Analysts have repeatedly said republican dissidents are likely to remain active and police have said the risk of attack, chiefly on security forces, was severe.

Tuesday's bomb was abandoned outside the police station in the early hours of the morning, forcing dozens of families to flee their homes before being disabled by army experts and declared a "viable device" almost 20 hours later.

"Yet again these cowardly criminals have shown complete disregard for the safety of the people of South Armagh and for police officers who serve this community," local police commander, Chief Inspector Sam Cordner said in a statement.