A Polish court has refused to transfer a Ukrainian suspect wanted by Germany in connection with the Nord Stream gas pipeline explosions back in 2022, with the country's leader, Donald Tusk, saying: "The case is closed."

Germany's top prosecutors' office says Volodymyr Z - whose full name isn't given, but has no known link to the Ukrainian president - was one of a group suspected of renting a sailing yacht and planting explosives on the pipelines near the Danish island of Bornholm.

The explosions largely severed Russian gas supplies to Europe, representing a significant escalation in the Ukraine conflict and worsening of the continent's energy supply crisis.

The suspect faces allegations of conspiring to commit an explosives attack and of "anti-constitutional sabotage".

"The person being prosecuted, if he was the perpetrator, is entitled to functional immunity, which covers an act committed in connection with his activities for the Ukrainian state," judge Dariusz Lubowski said in his verdict that ruled the German application was not admissible.

"If Ukraine was indeed the organiser of this act of aggression, then only Ukraine can be held responsible for this event."

Ukraine has denied involvement in the explosions.

Earlier this month, Tusk said it wasn't in Poland's interest to hand the suspect over to Germany.

"Polish court denied extradition to Germany of a Ukrainian national... and rightly so. The case is closed," Tusk said on X following the verdict.