Polish pipeline operator PERN said on Saturday the oil flows via the damaged segment of the Druzhba pipeline have been restored.

"PERN's technical services restored the full functionality of the damaged pipeline used to deliver crude oil to the company's German customers on Saturday," PERN said in a statement.

"An investigation into the cause of the leak is ongoing," it added. 

The leak in the pipeline which was detected near the village of Zurawice in central Poland has caused the flow of oil deliveries to be halted for three days.

The Polish operator had previously stated there were no signs of third-party interference in instigating the damage and that preliminary checks indicated the leak was possibly an accident. 

The Druzhba (Friendship) pipeline network began in the 1960s and pumps oil from the Urals to Europe through a northern branch via Poland and a southern branch via Ukraine. It is the world's longest oil pipeline and one of the biggest oil pipeline networks in the world. It carries oil some 4,000 kilometers from the eastern part of European Russia to points in Ukraine, Belarus, Poland, Hungary, Slovakia, the Czech Republic, Austria, and Germany, but mainly supplies the Schwedt and Leuna refineries in Germany.

This comes after the Nord Stream gas pipelines were damaged by two explosions first, followed by a third and then a fourth, according to Danish officials during a NATO conference on September 28, with the first two caused by the force of around 1,100 pounds (500 kilograms) of TNT each, according to The Wall Street Journal, citing persons familiar with the case.

Russia's Nord Stream gas pipelines were struck in Danish waters near the island of Bornholm on September 26. The general agreement was that the explosions were the result of sabotage, and Russian President Vladimir Putin blamed Ukraine for causing it.

In light of Europe's energy crisis, the recent gas leaks have worsened the energy crisis by further decreasing the supply of gas in Europe. 

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