The Revenue's Customs Service has found an illegal fuel-laundering plant with the potential to cost the Exchequer millions of euros per annum.
About 30,000 litres of washed diesel, an oil tanker, a forklift truck and other equipment was seized in the raid on the plant in Ballybinaby, Co Louth.
The plant had the capacity to process 20,000 litres of cheaper agricultural-use diesel per day.
Two men, found on the site, are being questioned.