Cold war all over again…

Russian submarines and spy ships are aggressively operating near the vital undersea cables that carry almost all global Internet communications, raising concerns among some American military and intelligence officials that the Russians might be planning to attack those lines in times of tension or conflict.

The issue goes beyond old Cold War worries that the Russians would tap into the cables — a task American intelligence agencies also mastered decades ago. The alarm today is deeper: The ultimate Russian hack on the United States could involve severing the fiber-optic cables at some of their hardest-to-access locations to halt the instant communications on which the West’s governments, economies and citizens have grown dependent.

While there is no evidence yet of any cable cutting, the concern is part of a growing wariness among senior American and allied military and intelligence officials over the accelerated activity by the Russian armed forces around the globe. At the same time, the internal debate in Washington illustrates how the United States is increasingly viewing every Russian move through a lens of deep distrust, reminiscent of the Cold War.

Inside the Pentagon and the nation’s spy agencies, the assessments of Russia’s growing naval activities are highly classified and not publicly discussed in detail. American officials are secretive about what they are doing both to monitor the activity and to find ways to recover quickly if cables are cut. But more than a dozen officials confirmed in broad terms that it had become the source of significant attention in the Pentagon.

“I’m worried every day about what the Russians may be doing,” said Rear Adm. Frederick J. Roegge, commander of the Navy’s submarine fleet in the Pacific, who would not answer questions about potential Russian plans for cutting the undersea cables.

Cmdr. William Marks, a Navy spokesman in Washington, said: “It would be a concern to hear any country was tampering with communication cables; however, due to the classified nature of submarine operations, we do not discuss specifics.”

In private, however, commanders and intelligence officials are far more direct. They report that from the North Sea to Northeast Asia and even in waters closer to American shores, they are monitoring significantly increased Russian activity along the known routes of the cables, which carry the lifeblood of global electronic communications and commerce.

Just last month, the Russian spy ship Yantar, equipped with two self-propelled deep-sea submersible craft, cruised slowly off the East Coast of the United States on its way to Cuba — where one major cable lands near the American naval station at Guantánamo Bay. It was monitored constantly by American spy satellites, ships and planes. Navy officials said the Yantar and the submersible vehicles it can drop off its decks have the capability to cut cables miles down in the sea.

“The level of activity,’’ a senior European diplomat said, ‘‘is comparable to what we saw in the Cold War.”