To enable a takeover, Orlen in 2022 agreed to sell some Lotos assets to companies including Saudi Aramco and Hungary's MOL to fulfill European Union antitrust rulings and meet conditions for taking over the Gdansk-based firm.

Orlen's purchase of Lotos was part of a plan by the then ruling Law and Justice (PiS) party to increase control over the economy and create 'national champions'.

"NIK...draws attention to the abnormally low price for the sale of Grupa Lotos' assets - at least 5 billion zlotys below the estimated value," the office said in a statement.

It also said that the sale of Lotos' Gdansk refinery to Saudi Aramco threatened Poland's energy security.

Following a change of government, prosecutors launched two probes into Orlen in January, one concerning alleged malpractice resulting in losses during its takeover of Lotos, and another into claims that it artificially lowered petrol prices before a 2023 election to help PiS.

($1 = 4.0286 zlotys)

(Reporting by Marek Strzelecki, Pawel Florkiewicz, Alan Charlish; Editing by Kirsten Donovan)