(Adds Eni statement)
MILAN, March 31 (Reuters) - Five staff at a treatment plantoperated by oil major Eni were placed under housearrest on allegations of illegal waste trafficking, the Italianpolice said on Thursday.
The arrests, of managers and workers, are part of atwo-year-long investigation by regional anti-mafia prosecutorsinto waste management at the plant in southern Italy, a policestatement said.
The plant is located in the Val d'Agri oil concession areain the Basilicata region, in which Royal Dutch Shell has a stake.
The police said part of the plant had been seized and that the alleged illegal activity had allowed the Italianstate-controlled oil major to make "an unjust profit".
Eni pledged full cooperation with magistrates, adding it hadtemporarily suspended the arrested workers and was concludinginternal checks of its own.
Production at the field of around 75,000 barrels per day hadbeen halted for the time being, Eni said.
"Eni confirms... respect of legal requirements and bestinternational practices," it said.
(Reporting by Stephen Jewkes; editing by John Stonestreet andSusan Fenton)