Belarus state energy company Belneftekhim said earlier that it had partially resumed oil transit towards Poland and that its daily Western-bound transit plan for June was 65,000 tonnes.

PERN said regular volumes of oil flows were expected in July.

"The first phase of the system operation will last until the end of June. This means that crude oil supplies will be delivered in smaller volumes - acceptable to PERN customers," PERN said in a statement.

PERN clients include two Polish refineries - one in Gdansk, owned by Lotos and one in Plock, controlled by PKN Orlen, as well as two plants in Germany.

Poland's state-run PKN and Lotos have relied on seaborne oil supplies and oil inventories to keep their refineries working during the suspension of Russian deliveries.

In May, Moscow agreed to pump dirty crude back from Belarus to clear the pipeline. Refineries in Poland and Germany agreed to process the dirty oil sitting in pipelines west of Belarus.

Earlier this month, Russian officials and oil suppliers met European buyers in Moscow and decided that compensation for the contamination of Russian oil in the Druzhba pipeline should be agreed between buyers and sellers.