German Defence Minister Boris Pistorius said damage to two undersea cables in the Baltic Sea looks like an act of sabotage.
A 1,170km (730-mile) telecommunications cable between Finland and Germany was severed in the early hours of Monday, while a 218km internet link between Lithuania and Sweden's Gotland Island stopped working on Sunday.
The incidents came at a time of heightened tension with Russia, and Pistorius said "nobody believes that these cables were cut accidentally".
The Swedish and Lithuanian defence ministers said they were "deeply concerned" that the cable connecting their two countries had been cut.
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