A leak has been detected in an oil pipeline in Poland which is the main route through which Russian crude oil reaches Germany, Polish operator PERN said.

The firm said it detected a leak in the Druzhba pipeline, which originates in Russia, on Tuesday evening about 45 miles from the central Polish city of Plock.

It said the cause of the leak is not known.

The incident follows leaks late last month in the Nord Stream 1 and 2 gas pipelines running along the Baltic seabed.

Firefighters are working at the site of the leak, PERN said.

A Polish government security official, Stanislaw Zaryn, said the leak could be the result of an accident, but that officials were still investigating and looking at another possible explanations.

“Different scenarios are possible. We don’t exclude any of them,” he said.

The Druzhba pipeline, which in Russian means “Friendship”, is one of the world’s longest oil pipelines, and after leaving Russia it branches out to bring crude to points including Belarus, Ukraine, Poland, Hungary, Austria and Germany.

Last year, Russia accounted for some 35% of Germany’s crude oil supply.

But that proportion has been reduced following the Russian invasion of Ukraine, and the country’s focus now is on phasing out the remaining supplies before a European Union embargo on most Russian imports goes into effect.

A month ago, the German government took control of three refineries owned by Russia’s Rosneft, which account for about 12% of Germany’s oil refining capacity.