Two men aged 40 and 48 have been arrested as part of a Customs investigation into illegal fuel in Co Tyrone.
The pair from Coalisland were detained after police and HM Revenue and Customs officers searched three commercial premises in the Dungannon area on Thursday.
They have since been released on bail.
Around 1,000 litres of suspected laundered diesel were seized along with a van and tank.
John Whiting, HMRC assistant director for criminal investigation, said: "The production of illicit fuels is organised fraud, robbing taxpayers of millions each year in unpaid duty and VAT, as well as the waste by-product damaging the environment."
HMRC investigations are continuing.