Four men are being questioned at garda stations in the midlands after guns and ammunition were seized.
Gardaí suspect the men are from South America and part of a so-called "hit team" contracted to shoot someone.
Armed officers from the Emergency Response Unit intercepted the four early this morning outside Clara in Co Offaly.
Three of the men were travelling in a van, the fourth separately in a car.
They were armed with a machine gun, a sawn-off shotgun and several rounds of ammunition.
The men were targeted by An Garda Síochána's Security and Intelligence section which also investigates subversive crime.
The unit suspects the "hit team" was contracted to shoot someone as part of an ongoing feud among criminal gangs within the travelling community.
Gardaí said the feud escalated because of a failure to pay a small drugs debt, less than €100.
They believe the four are from Brazil and in their 30s but are trying to establish their identities and how long they have been in Ireland.
Searches have been conducted at addresses in Dublin.
The four are being questioned at garda stations in Tullamore and Portlaoise and can be detained for up to three days.
One of them was due to leave Ireland tomorrow.