Two men have been arrested following the discovery of fuel laundering plants in counties Monaghan and Louth.
The plants, which are located near Carrickmacross and Muff, had the capacity to launder up to 20 million litres of fuel per annum, a Revenue spokeswoman said, at a potential loss of €10 million annually to the Exchequer.
Some 40,000 litres of laundered fuel was seized at the Co Monaghan facility, along with bags of bleaching agent, a Mercedes car and a lorry with a concealed tank, which the Revenue said was used for delivering the laundered product.
Thousands of litres of toxic waste were also discovered at the site.
A quantity of oil, two vans and a lorry with a concealed tank were seized from the plant in Muff.
Two men, aged 54 and one aged 47, have been arrested in connection with the discoveries and are being questioned at Carrickmacross Garda station.