Polish Prime Minister Donald Tusk warned that the end of Russia’s war in Ukraine might lead to efforts to rekindle economic ties with Russia — including the restarting of the controversial Nord Stream 2 gas pipeline.

As Europe faces the possibility of peace negotiations between Russia and Ukraine, Tusk described calls by European politicians to rebuild ties to Moscow at the eventual end of the war as “an alarm bell.”

“[I know] it means that someone in Europe wants to restore Nord Stream 2, to have good business with oil and gas from Russia, and so on,” he said. “For me, it’s always like an alarm bell,” Tusk said in an interview with the Sunday Times.

A major pipeline transporting gas from Russia to Germany via the Baltic Sea, Nord Stream 2 is described by critics as a strategic mistake and a symbol of Europe’s appeasement to Moscow.

The pipeline was blown up in 2022 after the start of Russian President Vladimir Putin’s full-scale invasion of Ukraine. A Ukrainian professional diver was later arrested over his suspected involvement in the sabotage.

“The problem with North Stream 2 is not that it was blown up. The problem is that it was built,” Tusk wrote on X social media earlier this month.

In the Sunday Times interview, Tusk said that a Polish court ruling blocking a German extradition request for one of the suspects in the Nord Stream sabotage means that Ukraine has a right to attack Russia-linked targets anywhere in Europe.

The Polish leader also berated Europe’s complacency and its constant underrating of Putin’s expansionist threats. “We are talking about the end of the era of illusions in Europe — too late, I’m afraid. Too late to be well prepared for all the threats, but not too late to survive,” Tusk said.

Also in the interview, Tusk described Britain’s exit from the EU as “one of the biggest mistakes in our [shared European] history”— 10 years after U.K. Prime Minister David Cameron’s ill-fated attempt to use the Brexit referendum as leverage to extract concessions from the EU.

“And today I think it’s much more visible,” said Tusk, who was well-steeped in the first phase of the Brexit negotiations as president of the European Council at the time.

 “Especially after Brexit, Poles realized that the objective situation in the U.K. is not much better than in Poland. I also know that Brits are starting to leave the U.K. and begin a life here in Poland,” he said.