As was warned about, years ago:
Top Secret Brief: Russian Threat to Undersea Cables Growing
Russian Presence Near Undersea Cables Concerns U.S.
U.S. Shadowing Russian Ship in Atlantic Near Nuclear Submarine Areas

Stuart Peach / Getty Images
Air Chief Marshal Sir Stuart Peach, the head of Britain’s Armed Forces, told a group of military insiders that the risk of such action is grave and potentially catastrophic.