Russia has made significant cuts to oil supplies sent to German refineries recently, rekindling concerns in Germany over the reliability of Russian energy supplies.

Lukoil, Russia's second-largest oil producer, yesterday said that supplies to Germany had been reduced by about one-third in July and August, but refused to explain why.

Analysts said that Lukoil's decision not to provide previously contracted quantities of oil could be aimed at extracting higher prices from German refineries, or it could be part of Lukoil's efforts to acquire stakes in German and European refineries.

Germany's economics ministry said that the country's energy supplies were not in danger, as refineries could turn to other oil suppliers to make up shortfalls.

The Schwedt refinery north-east of Berlin said that supplies via the Druzhba, or "Friendship", pipeline from Russia had been reduced, but "talks were under way" with Russian oil companies.

"The situation is not dramatic," a spokesman said, adding that the refinery had increased supplies from the North Sea in recent weeks.

Germany's MWV oil industry association said that Russian supplies had fallen in June and July but stressed that refinery production had not been hit. Germany receives about a fifth of its oil supply via the Druzhba pipeline.

Russia in January briefly suspended oil supplies through the Druzhba pipeline following a pricing dispute with Belarus.

Transneft, the Russian oil pipeline monopoly, said that it was fulfilling its contracts to refineries served by the Druzhba pipeline. Transneft's Sergei Grigoriyev said: "Transneft has not reduced any deliveries. We are working to a normal regime." Lukoil said that the company would next week explain the cutbacks but noted that there was still time to make up the shortfall for the month.

Oil traders said that a dispute between Lukoil and Sunimex, Germany's biggest oil importer, might account for the supply cut, but the aggressive Russian strategy to acquire European refining assets could also play a role.