Repairs on the pipeline carrying Russian oil to Germany have begun and Poland does not think the incident was sabotage, the top Polish energy security official told Reuters on Thursday.

The discovery of a leak in the main route carrying oil to Germany, which operator PERN said it found on Tuesday evening, came with Europe on high alert over its energy security in the aftermath of Moscow's invasion of Ukraine.

"Everything points to natural causes, material fatigue, of course the fractured section will be examined. So at this moment we have no information that could point to sabotage," Mateusz Berger, secretary of state in charge of strategic energy infrastructure said in a telephone interview.

PERN said it aimed to resume pumping oil to Germany at "full levels" as quickly as possible, adding the next update on the status of the situation would be published in the evening.

Berger said the leak was caused by a "relatively large" fracture along the pipeline, adding that repairs have already started. He declined to give further details.

PERN said late on Wednesday it had located the site of the leak and initial findings showed no signs of interference by third parties.

Polish Prime Minister Mateusz Morawiecki had earlier on Wednesday told public radio that it was too early to say whether the leak was accidental damage or caused by sabotage.