The ministry said this month it had released 800,000 tonnes of crude from reserves to maintain regular output at Polish refineries.

"In my opinion this is sufficient for now and deliveries are being supplemented via Naftoport," Energy Minister Krzysztof Tchorzewski told reporters.

He added the polluted oil was being partly mixed with clean oil and used in refineries.

"We have started cleaning the pipeline system of the contaminated oil," the minister added.