A leak was detected in an underground oil pipeline in Poland which is the main route through which Russian crude reaches Germany, the Polish operator said on Wednesday.
The operator, PERN, said it detected a leak in the Druzhba pipeline on Tuesday evening about 70 kilometres (45 miles) from the central Polish city of Plock.
It said the cause of the leak wasn't known.
The incident follows leaks late last month in the Nord Stream 1 and 2 gas pipelines running along the Baltic seabed, and amid an energy standoff between Russia and the West.
A Polish government security official, Stanislaw Zaryn, said it was too early to speculate about the causes of the leak as experts investigate the matter.
“All hypotheses are possible,” Zaryn tweeted, adding that “the scale of the failure does not affect the safety of the Republic of Poland.”
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.
Firefighters were working in cornfields near the village of Zurawice to determine the exact point of the leak, according to a spokesman for firefighters, Brig. Karol Kierzkowski.