GARDAI suspect that the bomb left beside the Sinn Fein office in Monaghan town yesterday was planted by loyalists.
Army explosives officers will carry out tests on the device today. It is understood the device contained some 2.5 kg of a substance which is suspected to be old commercial explosive and which failed to detonate.
Security sources said the bomb was crudely made, and similar to other devices produced by loyalists before their ceasefire in October 1994.
In that year, the UVF unsuccessfully attempted to detonate two bombs in Dublin.
The device was found after it partially exploded yesterday morning.
A man living in a flat near the Sinn Fein office in Dublin Street, Monaghan, heard a loud bang at around 9 a.m. When he went to investigate, he found a hold-all with wires and a grey white coloured substance inside.
The area was sealed off for most of yesterday While an Army bomb disposal team travelled from Dublin to examine the device. The EOD (explosives ordnance disposal) team examined the device before removing it for further tests.
Gardai said they believe the bang heard by the resident was the detonator of the device going off.
An officer said the device was planted in an archway under the offices. The donation of 2.5 kg of commercial explosive could have caused considerable damage to property.
It is thought the device was planted during the hours of darkness, with a timer set to detonate it between 9 a.m. and 9.30 a.m.
It is understood there was no one in the Sinn Fein office when the explosion took place. The local Sinn Fein representative, Mr Caoimhghin O Caolain, was attending a meeting of Monaghan County Council at the time.
There was no claim by any loyalist group about the incident and no comment from Sinn Fein.
However, the RUC has confirmed that at least two other booby trap bomb attacks on republicans in the North since the New Year were carried out by loyalists.
Neither attack was admitted by the loyalists but the RUC says it is satisfied that the UDA was responsible.
The loyalist paramilitary organisations are officially maintaining their ceasefire but sources close to the leaderships have indicated that there could be "one off" unclaimed attacks on republicans if the IRA continued its violence.
The incident yesterday caused some concern among the Defence Forces about the availability of EOD teams for operations at the Border. After the IRA and loyalist ceasefires in 1994, a decision was made to reduce the Army's EOD commitment and the permanent bomb disposal team which was kept at Aiken Barracks in Dundalk was removed, as was another unit at Limerick. A team remains in place at Finner Camp in Co Donegal.
The team which disposed of the device yesterday is based at Cathal Brugha Barracks in Dublin and took just under four hours to arrive.