A dissident republican group is believed to be planning a bomb attack in Northern Ireland to disrupt progress towards a political settlement.
Gardai believe the bomb may still be in the Republic and appear to have been aware of its existence for more than a week.
Raids on the homes of suspected dissident republicans took place last weekend as part of a Special Branch operation to track the bomb. But nothing was found.
It is believed the bomb may have been constructed in the mid-west area earlier this month and moved northwards.
It is also understood that the group calling itself the Continuity IRA may be behind the bomb plot. This group has had close links with the "Real IRA" group responsible for last August's Omagh bombing.
The Continuity group is known to have become active since the start of the year, mounting ineffective attacks on security targets inside Northern Ireland. Several of its members have been arrested there.
Gardai have also detected a rise in activity among the group's members in the Republic. The Continuity group has a national organiser, a Cork man who may be living in the midlands, and he is reported to have been very active in recent months.
It is believed this man may have put together a bomb-making team, possibly with a base in the Roscommon area. The group is known to have support in the Leitrim/Cavan area.
It was also closely allied to the largely south Armagh/Dundalk-based "Real IRA". This group mounted several similar bombing operations last year timed to damage the political talks.
The Dundalk-based bombers were twice intercepted by gardai as they tried to mount attacks in the days before the Belfast Agreement on Good Friday last year, and also just before St Patrick's Day.
After the Omagh bombing, the group calling itself the "Real IRA" disintegrated in the face of adverse public opinion and a major Garda investigation. It called a ceasefire but the Continuity group refused to do so.
As part of the Omagh investigation, gardai discovered that there was dual membership between members of the Continuity IRA and "Real IRA", the two groups sharing expertise and personnel.
It would appear that the Continuity group has now assumed the role of leading republican dissent against the Provisional IRA ceasefire and Sinn Fein participation in the talks at Stormont.
Garda sources also report an increase in Provisional IRA activity, and suspect it may have been involved in firearms training in the Slieve Bloom area in the past month.
However, sources say there is no indication that the Provisional IRA is about to break its ceasefire.