It is understood the arrests are part of the ongoing garda operation against republican dissidents. The three men, all in their 20s, were detained during a series of early morning arrests in Counties Louth and Monaghan and are being questioned in Monaghan town garda station.
Dissident republicans are opposed to the current peace process in Northern Ireland.
One man has so far been charged in connection with the Real IRA blast in 1998 which killed 29 people and injured hundreds more. Colm Murphy, a publican and builder from Dundalk, County Louth, has been charged at Dublin's Special Criminal Court with conspiring to cause an explosion. Last week four men were named by the BBC's Panorama programme in connection with the car bomb. The documentary produced evidence which it claimed linked the four to mobile telephones used in and around Omagh on the day of the atrocity. Man injured in paramilitary-style attack Bomb blast children 'lucky to be alive' Links to more Northern Ireland stories are at the foot of the page.