Dissident republican violence is expected to increase in coming months following the weekend bombing outside BBC Television in London, according to senior security sources.
The dissidents, in the Continuity IRA and "Real IRA", are working in unison, although they remain separate organisations, according to Garda sources.
It is believed the anti-agreement republicans intend stepping up their violence in an attempt to wreck the political structures in Northern Ireland during the run-up to the British general election. Both groups are said to have grown in strength and sophistication.
It is believed the dissidents have large bombs in place in the Border area, and this contributed to the RUC's decision not to send large numbers of police into south Armagh to enforce the exclusion zone around the foot-and-mouth-infected farm at Meigh.
Yesterday morning's explosion in London is the largest attack to date, although the dissidents are believed responsible for the booby-trap device which blinded a 14-year-old boy last month.
Scotland Yard's anti-terrorist chief, Deputy Assistant Commissioner Alan Fry said only prompt action by the emergency services had prevented devastating consequences from the blast. A London Underground worker was injured.
Bomb-disposal officers had been attempting a controlled explosion when the device - concealed in a taxi, packed with between 10lb and 20lb of high explosives - detonated about 12.30 a.m. The blast knocked pictures off walls in homes up to a quarter of a mile away. A telephone warning was received at 11.22 p.m. at a London hospital.