Gardai were yesterday questioning five men arrested after investigations in the Border area into the activities of republicans opposed to the Belfast Agreement.
It is understood that security forces on both sides of the Border have become concerned at the prospect of further attacks.
The men were arrested on Monday at 9 p.m. and are being held under the Offences Against the State Act in Cavan and Monaghan Garda stations.
In the past three weeks republicans have attacked an RUC barracks in Armagh and the headquarters of the British foreign intelligence service, MI6, in London.
Senior Garda sources have expressed concern that the group responsible for the attacks could carry out further acts of violence before this weekend's annual conference of the Ulster Unionist Party in Belfast.
The republican terrorists have tried on a number of occasions to upset the political process in Northern Ireland. The most recent attack, on MI6 headquarters at Vauxhall Cross in London, coincided with the important South Antrim by-election.
It is feared the republicans, who are largely based in the Border area but have spreading support among hardline republicans elsewhere, intend carrying out an attack on a security base in Northern Ireland.
It is suspected this could come either before this weekend's UUP annual conference or before the expected following meeting of the Ulster Unionist Council which might take place before the end of the month. A challenge to Mr David Trimble's leadership might be mounted at the UUC meeting.