Armagh-born Colm Murphy, 48, a building contractor who also runs a Dundalk pub, was charged with conspiracy with an unnamed person to cause an explosion under the terms of Ireland's Offences Against the State Act, between 13 and 16 August last year.
Mr Murphy, of Ravensdale, Co Louth, also faced a second charge of membership of the Irish Republican Army, an illegal organisation, on 14 August 1998. He was arrested on Sunday and held in custody for questioning under anti- terrorist legislation.
He spoke only to confirm his name. Mr Justice Frederick Morris, presiding over the three judges, remanded Mr Murphy in custody until 18 March pending a bail application.
Mr Murphy was one of five people detained last Sunday by gardai in the Louth and Monaghan area in connection with the Omagh blast last August, which killed 29 people.
Two further arrests were made in Dundalk on Monday. In a related operation the Royal Ulster Constabulary detained a number of men including the chairman of the 32 County Sovereignty Committee. A garda spokesman said last night three men were still being questioned, one in Monaghan and the others in Carrickmacross. The Garda investigation into the Omagh blast was based there until it moved to Garda divisional headquarters at Monaghan. The car used in the bombing was stolen in Carrickmacross in the Irish Republic, but detectives believe the bomb itself was manufactured in Northern Ireland.
The IRA was accused yesterday of being responsible for an attack on a woman in South Armagh during which a gang used a knife to carve a death threat on her arms and legs.
The woman was attacked by up to eight men, four of them reportedly with rifles, who forced their way into her home in the village of Bessbrook in the early hours.
Dublin newspapers reported yesterday that the Taoiseach, Bertie Ahern, was told earlier this month of two training camps opened by the Provisional IRA in the Irish Republic in readiness for a renewed campaign of violence if the peace process collapses.Reuse content