Gardai investigating the Omagh bombing were last night questioning four men and continuing a search for guns and explosives along the Border.
The operation is concentrating on finding arms dumps and those responsible for stealing the Vauxhall car which was used to carry the bomb to Omagh on August 15th. Senior Garda sources said they were hopeful of making progress on both fronts.
So far, about 20 people have been arrested and questioned in connection with the theft of the car in Carrickmacross, Co Monaghan, two nights before the explosion, which killed 31 people and seriously injured 200 more.
All those arrested have been questioned in Monaghan and Carrickmacross Garda stations by members of a 30-strong team of detectives and Special Branch officers detailed to investigate the activities of the dissident republicans responsible for the bombing.
While gardai are concentrating on finding those who stole the car and drove it to collect the bomb, the RUC is endeavouring to locate the bombers.
Last week the RUC arrested seven south Armagh men and questioned them about the bombing and about the "Real IRA", the dissident republican group which admitted responsibility for the bombing.
The Border search is concentrated in the area close to where officers found six rifles, including a Belgian-made FN sniper's rifle, a general-purpose machinegun, seven handguns and bomb and mortar parts in a field just off the Carrickmacross-Hackballscross road, about 150 yards south of the Armagh border.
The weapons are still being ballistically examined but, according to senior Garda sources, it appears that they belonged to the Provisional IRA, which declared a ceasefire last July and whose leaders condemned the Omagh bombing.
Although the Provisional IRA is maintaining a ceasefire, it appears that it has been keeping stocks of weapons, in good condition, close to the Border. The organisation is refusing to decommission any arms.
Aside from the Garda operations on the Border, Special Branch officers have been seeking people suspected of involvement with the Continuity IRA, the only paramilitary group, North or South, which has refused to declare a ceasefire.