Five men have been arrested in the Irish Republic on suspicion of trying to move explosives across the border.
It is understood shots were fired at officers in the Omeath area of County Louth.
The incident happened when Irish police stopped three cars as part of a planned operation against dissident republicans.
The five men are being held in police stations in Drogheda, Dundalk, and Balbriggan.
The three cars involved have been seized, and armed police have been searching premises near Omeath and Ravensdale.