Tomasz Zakrzewski, spokesman for the PERN company operating the Polish section of the pipeline, told the TVN24 channel that the company had sent a letter to the Belarusian operator of Druzhba last night but received no answer.
"We do not know yet why the oil supplies were suspended and when they will be resumed," Zakrzewski said.
Deputy Economics Minister Piotr Naimski said that although Poland's oil tap had been switched off, the European Union nation still had enough oil reserves to last 80 days.
"There is no direct threat to Poland's energy security because the country has oil reserves for 80 days," he said.
Russia's reliability as an energy supplier came into doubt when it cut off gas supplies to Ukraine in a gas price row early last year. Russia supplies more than 25% of the EU's oil and natural gas.
Russia doubled the gas price for Belarus to $100 per 1,000 cu m from January 1, and also imposed an oil export duty of $180.7 per metric ton for Belarus. The Russian ally responded January 3 by introducing a transit duty of $45 per metric ton of Russian oil from January 1.